Here's a good video on the protests (via Ezra Klein):

This may not be a coherent group with an organized set of demands, but I don't think they should be dismissed. They have a diverse, but real, set of problems. Health care costs (don't get me started on all the speech therapy that our insurance company refuses to pay), student loan debt, unemployment. There are a lot of videos on their Facebook page. 

Higher education and student loan debt is a huge part of this protest. Check out this blog post on an unemployed PhD on the We Are the 99 Percent tumblr blog. Dude, I'm totally going to this protest!