There's a small problem when preserving file modification times - some backup programs will often not realize that the file has changed. Not only is the time preserved but quite often the file size as well and many backup programs don't look beyond those criteria.
It would be nice if there were an additional option to "bump" the mod time by just a second. Then the approximate time is preserved, without it being exact. It's nice being able to maintain the date/time for the many music organizers that can display new music or that allow you to browse your music by the mod date.