Okay, I could be totally wrong here, and I invite correction, but if I'm right, we have our first real indie social game hit.
Stick Run is by Otto Manuel, who has done a series of Flash-portal games, some of which are pretty good, like StickCombat.
Stick Run is a somewhat frustrating sidescroller with, really, only two buttons; jump and crouch. You move automatically left-to-right, and must avoid obstacles in your path. Anything you hit is instadeath. In some cases this is tricky, e.g., jump too soon and you hit an upper obstacle, but not soon enough and you hit a lower one. Graphics are stick-figure primitive, gameplay is fast and brutal, and the music (unusually for social games) does not suck.