One solution that is employed by some sites (SBNation, for instance) is to have a period of time (a day or a few days) after signing up before a person is able to comment. That way genuine new users are forced to lurk a bit and learn the ways of the community and it could also prevent things like the people creating burners just to come say stuff they aren't willing to associate with their real name. You'd also largely prevent stuff like the Reddit invasion on SOPA day, etc.