In the GreenfootGallery, they use a voting system that i have not seen implemented before, but works suprisingly well. First, you can only vote for programs you like. Programs are rated by the amount of votes, not by a rating system. The second, is that they use a formula that combines votes/views/recent votes/recent views/new updates in order to come up with a 'popularity' rating that also is a good estimate of general interest on the site. The thing that seems to protect it from malicious intent is that you can really only give programs positive press, the worst way to affect a program is to ignore it completely.