While I agree, if you listen to it often enough to warrant keeping a copy around, (and the means are available), pay for it. The other side of the coin that gets overlooked a lot of the time by people that assume that musicians are just out to make a buck with the music they put out on MP3 is that sometimes people are just getting started, or just want more airplay or really, for whatever reason, they *want* people to have access to their music for free. Not every musician is a star performer that everyone's grandmother has heard of. There are even, in fact, people who play and record just for fun. Especially now that you don't have to record to tape, and it doesn't necessarily cost a fortune to get your music out. So perhaps some of you folks out there with the paramilitary attitudes towards music sharing need to lighten up. As long as you've got the proper permissions, and you're covering whatever costs you are being asked to cover, I think music sharing is fine, and in general, MP3 can be a fine format to use to share in. It's compact, the sound is decent(OK, so you might not want to record the London Symphony Orchestra at 64Mbps, but set up correctly it works fine.) and its a free format to record in.
One other note to 'mittens': not everything on you hear is available on CD. The virtual cornucopiea of relaxing electronica that puts me to sleep at night, as well as the other dance and trance music that is available on the net is a royal PITA to get ahold of unless you are into the dance/trance/rave scene, which, as a 34 year old with 2 kids, I am not.