You don't think throwing up a 300x250 banner on the front page from somewhere like RightMedia could get a premium site like reddit $2 CPM? I bet even low traffic quality sites like icanhazcheesburger or cracked are getting more than $2 CPM.

By the way, reddit can really learn from Demand Media sites like Cracked, who are very very good at monetizing the same type of low quality social media traffic.