Does anyone remember what happened to Myspace? Of course it was complicated, but I think the primary driver in the exodus from Myspace to Facebook were the perceived privacy benefits of Facebook. People do care about privacy, but will only act on it if there is a reasonably convenient alternative - if Diaspora can make itself convenient, I think it has a chance.

Also, add in a slow news week with some sensationalized mainstream stories about privacy that mention Diaspora, and I think the odds increase even more. People love to have something to be paranoid about with their friends.