It's different: it's a recommendation of our product and it drives real clicks back to Mixpanel (excluding google). Powered by badges are extremely common and are more akin to an ad. The main difference is that Rapgenius' sole goal is to game Google, ours is not.
it's actually not - Matt Cutts specifically made a video about these exact type of "widget" links a few months ago. He recommended that they be no-followed.
I don't understand how stat counter gets away with what they do. They offer stats similar to google analytics. They seem to get most of their ranking from including a link back to them with a random anchor text from a set of terms they want to rank for in the JavaScript block to install stats.