I listen to my -q5 Vorbis files on an iRiver iMP-550 with a pair of Sennheiser PX-100 headphones.
At home, I listen to my FLAC -8 files on the computer over the on-board sound card SiS 7012 (built by Realtek) and a pair of Trust loudspeakers - sorry, I don't know the exact name, but this is what they look like:
It's a PHP script I wrote which generates an image with help of the GD extension.
I'm listening to my --insane Musepack library on the computer with a pair of Sennheiser HD 570 over a Terratec Aureon 7.1 Space 
I'm still waiting for any - and I really mean any - portable to support Musepack. I think I'd be the first to buy one!
I'm using foobar2000 as player and have an audioscrobbler account which calculates some nice statistics regarding my listening habits 
I output my 256kbps CBR Fraunhofer MP3's from my SoundBlaster Audigy into this badboy....
edit Yeah, I use Audioscrobbler too!
File Format: I'm mostly listenig to mp3 vbr q3 (lame). I tried to use .ogg, but then I purchased an...
Portable Device: iPod color 20GB. I'm using it less for walking around than taking it into my car and plugging it in with an mc-adapter.
PC: I plugged my built-in sound device of my asus a7n8x-board into my sony-amplifier, which is connected to two "stand-alone" loudspeakers (with about 80W I guess).
Apps: Winamp (Modern Skin, Cover&Tag Plugin), MP3Tag of course, Easy CD-DA-Extractor for converting an ripping, Sebastian's Amazon Cover Downloader and Goldwave for editing.
Utopian wishes / I'm hoping that...: (1) new explorer functions in windows vista are going to make music-libraries superfluous (2) iTunes is going to support folder.jpgs and alternative file formats.
So long
Files: MP3s (LAME 3.96.1, 192 kBit/s, Stereo, High Quality)
PC: Onboard sound with cheap boxes and the program Winamp 5.1
Portable device: Mobiblu DHH-100 5 GB
I am now using a Logitech USB Headset and switched from Vorbis / FLAC to MP3 / WavPack. Audio player is still my beloved foobar2000. 
I am listening my mp3 files from PC with Audigy sound card.
PC is conented with Kenwood RXD 355
It's just fine for me, I dont wont to heart my hearing.
Files: mp3, mostly LAME vbr q2
Apps: amaroK, mp3tag v2.36d via wine
PC: onboard sound chip + 5.1 amplifer on digital-out
Portable: old Sony Mp3-CD Player
Edit: mp3tag v2.36+ is working under wine now
Soundcard: Creative Audigy 2ZS
Speakers: Klipsch ProMedia Ultras 5.1 ... Dual 8" drivers in the subwoofer....
Ok here we go from Sweden
mp3 192-256 vbr High (lame) or mp3 320 alt preset CBR (lame)
Apps = DBpowerAMP (registred) , Winamp and MP3Tag 2.39
Mostly i use my modded xbox connected to one of my computers (xbox media center, hxtp://www.xboxmediacenter.com)
Amp = Yamaha rx-v550 (hxtp://www.yamaha.co.jp/english/product/av/products/ht/rxv550.html)
Front = Mission 760i (hxtp://oldsite.mission-hifi.com/archive/76series/760i_760se.pdf)
Center = Jamo E 5cen.2
surround = Jamo A 320 (hxtp://jamo.com/Default.aspx?ID=5897&M=Shop&PID=17135&ProductID=17442)
SUB = audio pro Evidence mk2 (hxtp://www.audiopro.com/templates/audio_pro_products/?id_products=417)
2 Carstereo JVC (mp3-cd) KD-G411
portable
Samsung YP-T7Z, (hxtp://www.samsung.com.au/mp3/YP-T7.asp) this has to be upgraded soon 
SonyEricsson W800i 2 GB (hxtp://www.sonyericsson.com/spg.jsp?cc=gb&lc=en&ver=4000&template=pip1&zone=pp&pid=10245)
And my newest thing is one Thomson TM9670 (hxtp://www.thomsonlink.com/audio/TM9670-405.html)
I try not to listen to music on my PC - I rip only to have music for the car through an Ipod.
My home system though is something special...
Mark Levinson 390s CD Player
Madrigal CZ-Gel interconnects (bridging Kable)
Mark Levinson 334 power amps in Bridged mode
Kimber Select Kable 3035
B & W 802D
Soon be upgrading to the new Mark Levinson 54 reference power amps when they become available.
regards
Sean
In-house I listen to FLAC only. In my car and when travelling I use an iPod with my FLAC library duplicated to MP3.
My house is filled with
Slimdevices Squeezeboxes (Image, bedrooms & kitchen), feeding
Audioengine A5's (Image) or Acoustic Energy Aego M's (Image).
My listening room has a Slimdevices Transporter (Image) feeding these ATC's (Image).
Moderation: Changed large embedded images to links.I don't like headset, out of home (I work at home) listen to the gray noise -- so I use an old Pioneer sx-626 with homemade loudspeakers (and only two, no 5.1-like tricks); usually playing from laptop, what is my portable at the same time 
onboard audio or playing from pc through an old fashioned Terratec soundcard.
Fileformats: only ogg (q7-9 vbr), mpc, mp3 (in this order). Lossless are converted because of diskspace -- never write cd or dvd (what are so interesting in quality, has bought the original).
Progs are mostly Winamp (2.8) and Amarok; after tryed and used a couple of ripper I stand at CDex 1.5 for ripping, also for converting, and medieval cue splitter for splitting -- never editing, if a file is wrong, than wrong -> F8. I didn't find the last for clear junk data, repearing wrong headers. Tagging (after a lot of searching, trying) only with Mp3tag.
Tag (and other over-hyper-meta) data are from "manual" search only (if no cd/lp-cover at hand), always checking more sources, if available.
Controlling and monitoring with Total cmd and its lister...
For file format i'm not picky so i get whatever available. Usually Mp3 with 320KBPS or FLAC format.
My Mp3 player of choice is (and probably always be) Winamp.
My soundcard is incorporated in the Line 6 KB37 Midi interface and Keyboard.
My speaker set is the Logitech X230 2.1 system:
Whenever i want to listen without disturbing my parents i use my Pioneer SE-M390 headphones.
My portable Mp3 player is my cellphone, SE W910i.
DON'T BUY THIS PHONE, JUST TRUST ME ON THIS ONE.Hi i'm new to the forum
I mostly listen my music on my pc with a soundblaster xfi platinum and a sennheiser hd555 headphone set. Also i dont leave the house with out my ipod shuffle, its the 1gb model which is more than enough when im out
i listen most of all to alternative rock, indie, thrash metal, trip hop, post rock, instrumental and movie and game soundtracks
I'm new to this forum, and pretty picky about my audio.
On the computer I use Auzen X-Fi Prelude 7.1 with Creative MegaWorks THX 550 (500 RMS, just replaced MegaWorks 510D and had a heck of a time finding it, but no one else currently makes a comparable surround sound speaker system for music). All of my files are in flac format (what I use), wav format (for the car), and also in mp3-320 bitrate format (because the son's silly mp3 player doesn't support lossless formats). My weapon of choice for media player is KMPlayer 2.9.4.1435.
In the Jeep, I have an Alpine CDA-9827, with MTX MXA4001 amp, and 2x MTX 10" subs. My tunes are played via a Creative Zen Xtra (replaced hard drive with 160GB) on .wav format. This system is getting old, but still turns heads of those using much newer and more expensive systems. The sound is simply amazingly loud and clear.
I listen on my android phone and on my PC. I use Shure SE846 and iFi xDSD with my phone with Poweamp v3 as player. For audiobooks I use Smart Audiobook Player. On my PC I use the iFi xDSD along with Sennheiser HD650 and my player is TuneBrowser and MusicBee.
PC thru Audioengine
D1 24-BIT DAC/ HEADPHONE AMP https://audioengineusa.com/shop/components/d1-24-bit-dacheadphone-amp/
A5+ https://audioengineusa.com/shop/poweredspeakers/a5-plus-classic-speakers/
S8 POWERED SUBWOOFER https://audioengineusa.com/shop/subwoofers/s8-powered-subwoofer/
when I listen so do the neighbors 
neighbor friendly ATH-M40x https://audio-technica.com.au/products/ath-m40x/
I listen to music on my gaming laptop that i use for everything because it's powerful enough for it all, and i also have an SD Card i use for my MP3 Player which has an old style 90s file format but with bit newer tech with a screen, little speaker, Lossless Sound and LED touchpad 
it's pretty neat.
So the file system of the MP3 Player sorts it by the order you copy each mp3 to the SD Card lol so for big mixes i have to create multiple folders and put 25 songs in each folder to make it easy to just drag and drop each song into the folders and quick to scroll through the songs on my MP3 Player, but it also makes it easier to edit the metadata too so win/win 
and then i just slot my tiny SD Card in and listen when on holiday or on the go.
My fave players on my laptop is VLC and Real Player and with Real Player that's also my go-to for getting the music because of it's browser video download and it has a super fast converter so i can convert an entire album to MP3 in one go.
My home library is shared from my server to several devices in the house. Distributed audio is handled by analog and USB inputs to my trusty Pioneer Elite SC-79 home theatre receiver. The USB audio is used only in the main zone, the home theatre area. The analog is used for a second zone output to five different rooms using a distribution system. All can be managed using either the iTunes Home Server combined with Apple's Remote app, or using DLNA handled from the server using Asset uPNP from Illustrate.
My mobile listening device is an iBasso DX160 digital audio player. It uses an older version of Android OD (8.1) but since it is dedicated to just being a player this is more than sufficient. My current favorite headphone pairing are the KZ ZAX that fit just right and have a great sound signature for my listening taste. I have several player apps installed, it depends on what I'm doing and sometimes just my mood which one I use.
I have posted some reviews of these here for reference.
My work phone is an iPhone 12. It gets the job done, but isn't as flexible as Android. Yet surprisingly there are still some really good player apps that break the standards that Apple has established. Maybe I'll review some of those in the near future.
EDIT: I have started an iOS music player thread here.