What format are most people using, and why?

AIFF, what can I say, I've become an Apple guy.

Apple Lossless for 2 reasons.

1. like you stated, you can't tag a wav file
2. I decided for a variety of reasons to use iTunes on a Mac Mini so that is the logical choice, iTunes won't play FLAC files

I'm entertaining the idea of getting into PC audio as a source. Having said that I believe at this point I would go with Apple Lossless.

The reasons being (1) I plan on purchasing a 60gb iPod to listen to while running, at the library, etc. I say 60gb because I believe that it is the only iPod with a 64 bit buffer (i.e. lot's of complaints form people using lossless on the 30gb (32 bit buffer) that they experience skips in the music.

Reason (2) is that I understand that the Squeezebox 3 is compatible with Apple Lossless. Ideally, I'd like to connect it via the DAC input on my Cary CD player.

I think that the only downside to using Apple Lossless is that I'm running a Windows XP environment, if that is a downside...

FLAC. lots of live music in FLAC format on dimeadozen.com.

I use macamp lite to playback on my Mac.

Wave files. 24/96 wave files for all my analog recordings.Hard drive space is cheap and getting cheaper. I want my recordings preserved in the best format.