This isn't the same thing at all, but you may be interested in AudioScrobbler.
http://www.audioscrobbler.com/user/Nepenthean/Basically, it keeps track of all the songs you play on your PC (CD, MP3, etc.) and compiles statistics about it. When all of those stats from lots of users are put together, you can start to find music by other artists that may be similar to ones you like via other people's profiles. They also occasionally have free MP3 promos, and they work with Last.fm. I haven't used Last.fm much, but they seem to take what you like and play a custom streaming internet "radio" station for each individual user.
The one problem with AudioScrobbler is that sometimes their site is down for days on end. There have been weeks where the site was down 50% of the time. Other weeks they're up just fine 100% of the time, so it can be kind of a pain sometimes.
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