I was asked to describe how mixoff.org works by someone at TOMB.
As the artiste, you upload your multi-tracks and link ’em.
As the mixer, you download the multi-tracks and mix ’em.
In general, the artiste uploads to get feedback on the material as well as (mebbe) publicity, and the mixers upload their mix for critique, both from the artiste, and other mixers, and to compare their work to others/learn how others do it.
As the uploader, it can be a bit frustrating (both in prepping the tracks with basic gating and mebbe noise reduction, lengths, etc., and just think of the time involved in uploading a half gig or more), especially when you don’t get any takers. Me, I’ve a thick skin, and I want to offer support to the site so I upload so there’s some divergent content (the site tends to be modern-rock heavy).
As a mixer, it can take quite a while to download the stuff, and sometimes the comments can be a bit biting. Me, I’ve a thick skin there also (I know what I like), and I think it’s important to keep my hand in mixing others’ stuff, and give feedback and interaction in the process.