It's a nice idea and from what I've seen so far they've implemented it well. Admittedly I'm not likely to be getting mad exclusives from many people, but it looks like it would make managing such things very easy indeed. Also the public aspect of it does it's thing better than myspace / virb / whatever, so that's an added bonus. I only signed up half an hour ago, but it's pretty good thus far.
I think their current pricing plan is probably quite sustainable actually, they seem to have quite a lot of 'pro' users, and even those paying the least can presumably support a number of the free users.
5 uploads a month is enough to archive my radio shows there plus some random mixes and the like, so free suits me.
http://www.soundcloud.com/unsettla if anyone's interested...