Date field use & format?

How is the date field supposed to be used?

and what is the necessary format for the data in it?

I'm working on making the fields for our church's sermon MP3's make the most sense possible so maybe for each this is the date of the sermon, or maybe it is supposed to be some other date like date the file was created? I don't know.

Is there any good general resource on the various MP3ID tags, formats and how they are meant to be used?

As a suggestion, it'd be handy to have some sort of date picker for this field that helps us pick dates and fills them in with the correct format instead of it just being the text box on the tag panel.