Actually not to plug something thats not finished... but I'm building a site for linux multimedia users(video and graphics too) as a means for new users to 'ease the pain' of converting. The site is using drupal on a home server and is in testing at http://track100.com:8080 ... so no way would I host files yet ...I have a Windows driver site for now defunct Aardvark Audio soundcards (http://asg.hopto.org) ...and that can eat up a couple gigs of bandwidth a month alone... - but linking is definitely doable...and wav isn't so unreasonable only 20MB-40MB per-track - only a couple minutes with some sort of peer to peer thingy... I'm not sure what the legal requirements would be for keeping copyrighted stuff off the site though... I spent most of the weekend looking at COPPA junk... (and found some vandalism on some government sites privacy acts :) )
But I have a friend with a good site homerecordingconnection.com and the paid members ($24 a year) get 24MB of space... collabs have usually had a 'leader' responsible for selecting performers and stuff...people just load their versions into their profile or link to it... and the leader assembles and mixes everything.
Climb to the top of the charts! Play Star Shuffle: the word scramble challenge with star power.