Soundflavor DJ is an innovative application (Windows only at the moment) that builds playlists on the fly, depending the the type of music you're listening to. I haven't tried Soundflavor DJ out as I have yet to install Parallels on the iMac, but I can assume the experience will mimic the perfection that is Pandora.
Backed by the Adaptive Path guys, Soundflavor's product revolves around the "Soundflavor Recommendation Engine", which they claim to be an advanced song-level music search and recommendation technology. Fortunately, these guys were smart enough to retain the iTunes experience by making Soundflavor an iTunes add-on. The last thing I would want to do is use something other than my beloved iTunes.
At first launch, Soundflavor DJ scans your massive music collection and identifies them. If your songs are mostly pirated and have messed up or non-standard ID3 tags, Soundflavor might not work as expected (although they are working with Music IP to identify metadata). After that's all done you can experiment with the "Flavorizer" control which determines the number and variety of songs it will recommend based on the songs you already had in the playlist.
The DJ also has a feature for discovering new music on shared iTunes playlists, which is definitely a nice touch if you live in a dorm and can see 100+ shared playlists. The Soundflavor Recommendation Engine was the result of six years of research and development work, so it should work as described. Download it, give it a few hot laps and let me know if it can lap the 730HP Evo in here (at 9:50).