They really do have a lot of stuff. You don't need to sign up for anything to just browse or sample. And they're 30 second samples. Not bad. Their servers seem to be slightly overloaded right now for searching, but browsing is fast. Too bad you have to choose a genre as the first step in browsing. They have comedy and spoken word albums in addition to music, too.
It's certainly not as complete as a music store (no Husker Du, Sugar, or Bob Mould; no Foo Fighters; no Sebadoh, to pick things I might be interested in) but artists they do have seem to be complete (at least for the labels associated, I guess). No OOP stuff that I saw, either.
Altogether, not bad. I don't know that I'd pay $1 a song when its compressed in an as-yet nonstandard form (read ``can't play it on the empeg'') when I could go to the store and get uncompressed versions for less to a little more, depending, plus cover art and a nice piece of backup media. It might be nice for trying out new artists, though. It looks like it would be faster and easier to go through than CDNow was in its prime.
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Bitt Faulk