MikeB of GarageSpin pointed me in the direction of Kompoz, where he accurately describes it as “Apple’s GarageBand audio recording software meets MySpace Band pages, where the social network revolves around song projects.”
How It Works
Anyone can start the foundations of a song, which includes BPM, copyright, etc. After that people can add drums, bass, guitar, or whatever they want to your initial file you uploaded.
The beauty of this is it makes collaboration really platform independent. You can be using Cubase, Pro Tools, Logic Pro, GarageBand, or whatever other recording software you like. You just upload the MP3,WMA,WAV or whatever file and everyone can use it as it is mixed into the Kompoz mix file. As new files are added, the previous files are given a version number to keep track of the history and progress of the work. Very cool.
Social Network
Each user gets an artist profile page. Artists can search for projects by genre, by artist (other members), keywords and tags, and license type.
Once the artist has a project going, they can opt to get notifications when people add to the song, or send messages regarding the song.
Conclusion
All in all this site looks very promising. I picture this being used by a lot of those Songfight guys, since many of them already do something similar and have documented the process - albeit more manual.
I am definitely looking forward to watching Kompoz grow, and might even consider throwing some projects up there in the coming months for my side project.
Expect a very detailed hands-on review at that time.
Extras
Visit Kompoze.
Their FAQ page also pointed me to this funny YouTube clip:

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