I don't know. I know it's not a good example in this thread but look at the success of 4chan, or look at all the people who post on 4-ch, SaoVQ, iichan, 420chan, etc.
There is a lot of meaningful and fun discussion on those sites (except for the first) and people who understand anonymity, even now in year 2010. I know it can't be a success like Facebook or Twitter, since most people is plainly retarded, but it's not an impossible task to at least have a fun site running. You just need to find good ways to advertise to attract people who may like anonymity for good purposes.