Err, what, exactly, do you want to know?

I have data, bitch, and I know how to use it. What, pray tell, do you want to know?

Off the top of your head, what percentage of your songs:

a ) Each unambiguously fits into a single genre? These songs may, collectively, go into more than one genre, but each song is in only a single genre. You may specify the genre yourself, including "combination" genres like "Folk-Rock" or "Pop-Rock", so it's not a matter of precision.

b) Should be considered a member of two genres, where it is not more precise to combine the genres?

c) Should be considered a member of three or more genres, where it is not more precise to combine the genres?

For b) and c), please specify the genres.

I'd like to help you, honestly, but that sounds like an awful lot of work, and I'm not certain I fully understand what you're looking for.

Off the top of my head, my collection of 5000-odd mp3's ranges in genre from punk to pop to rock to hip hop to jazz to blues to classical to indie and pretty much almost anything else you can think of, but I'm not sure what you mean by the difference between a combination genre and two different genres.

Can you give examples?

In other words, when would you want to put one song into two different categories, rather than into a "combination" category?

Does anything belong in two (or more categories), or should everything like that be considered a blend of two or more categories?

As someone with something approaching 2,000 complete records in mp3 format, I can tell you that organizing by formal genre is a near useless exercise beyond say classical vs. rock vs. jack vs. hiphop, and even then there is overlap.

My music is organized of course by artist and album, but for listening purposes, I use playlists and organize by mood, which I find to be by far more practical.

"Ah...what kind of music do you usually have here?"
"Oh, we got both kinds. We got Country and Western!"

How do you determine mood? How do you organize by mood?

My mp3's don't really like to be categorized and pigeon-holed. They're individual and unique in their own special way.

(sorry, I don't really categorize my music collection - they're all arranged by author or album title. I have some loose mp3's that are classified into:

alt.rock, classic rock, classical, game noise, jazz, old electronica, oldies - and they're pretty distinct [aside from the game noise])

Purely based on personal feeling and utility. Step back and think about how you listen to music. For me, either I want to liten to a full album, or I'll say walk into my place after a long day of work, and think to myself -- boy, I really feel lovelorn for some reason. So I go to my "lovelorn" playlist. Or I really feel like playing air guitar, ergo "Air Guitar" playlist. Or man, I'm depressed and want to commiserate with my music, ergo "Hopeful Downers." Or say I want "Breathy Female Vocalists."

Point being, with playlists you can optimize your music to the way you listen to it. Perhaps you really listen purely by genre, in which case in the long run, playlists are still optimally because songs that fit multiple genres can go on multiple lists without dealing with the silly id3 genre tag that restricts the music.

(oh, I have a bunch of mix-cd's and mix-playlists organized by mood [mostly on my work laptop]:

angry,1,2,3,4..
background,1,2,3..
cold,1,2..
down,1..
evening.
morning
up)

Also, that way, the playlists remain disposable and modifiable, while keeping pristine directory structure and not screwing up the tags on your music.

I use playlists and organize by mood

I generally do the same thing.

How do you determine mood? How do you organize by mood?

For me, at least, it's purely subjective: how does the song / track make me feel.

This is why I feel perfectly comfortable having such diverse artists as Trancenden, Journey, the Buzzcocks, Built to Spill and Carl Orff on the same playlist, to furnish one example.

i just do Pop, Dance, whatever label they came with when i dl'd them, or by decade.

Ok, let's see. Half of my mp3s are classical, and I have given them only one genre label, "classical". If the whole tagging system were a little more advanced, I would probably give each classical mp3 three or more genres/labels. "Classical", the period, and the type of work (symphony, concerto, choral, chamber, etc).

When it comes to contemporary music I don't get too fussy with genres. I would probably be happy with one genre for about 75% of my contemporary music, and two genres for about 25% of my contemporary music.

I don't organize my music. Therein lies the secret of my success.

I will gladly go through my 25663 mp3/ogg/flac files and answer your questions, ortho, if you pay me.

Categories? What 20th century bullshit is that? Tags are the shit, man. Tags. And I can easily see 2 or more tags for well over a majority (of my 5000 mp3s), and three or more for a strong plurality.

iTunes' categories are not very applicable to the music I listen to. I prefer using its rating system to organize tracks and artists I enjoy and prefer to rehear.

I have about 4,500 tracks in mp3 format and usually just choose the genre that pops up by default when I import them, or I choose whichever one seems appropriate fron the default iTunes list. I mostly listen to whole albums when I want to really "listen" to the music or let iTunes/iPod play at random if it is just for background.