Itunes Genres: Are you a splitter or a lumper???

I guess this question extends beyond itunes, and to the "art of tagging" itself. However, itunes is what I know. In itunes, you can make up whatever genre you want for a track, or keep the one that was downloaded off the online dbase when you ripped the CD. This provides lots of flexibility, way too many options, shines the limelight on the "gray areas" between genres. It's also a potentially huge time sink! Why does it matter - well, if you want to listen to a random assortment within specific genres, you need to define your genres.

Lumper or splitter? I guess I'm a splitter, to the point that I reach the grey zones, then I'm a lumper. For instance, rather than a single "world music" genre, I have seperate genres for African, Brazilian, Cuban, Jewish/Klezmer, etc, I try to reserve "world" for blends of ethnic music, such as Afro-Cuban-Celtic, or whatever. I also created a genre called "Vocal-Contemporary", which a friend calls "Singer-Songwriter" for all the contemporary artists that are not really folk, but not rock either - essentially anything contemporary where you are really listening to the singer, not so much the whole (e.g. Joni Michell, Greg Brown). Whereas I do differentiate between bluegrass and folk - folk itself becomes a gray area which includes a very wide array. And how do you distinguish between rock, pop and "alternative"? Today's rock was yesterday's alternative! The edges do get quite blurry!!!

Itunes also has another category called "group", which could be used as a sub-genre. For instance, within folk one might have acoustic-instrumental, old timey, etc. Within classical one might have "baroque, concertos, symphonies" - if one cared to go that far.

How important are genres to you? Do you go to lengths to define them? Are you a lumper or a splitter? How do you deal with the grey areas? What are some unique genres you've created???