I would not agree on that, it seems to me that github is used differently than sourceforge or the like. The vast majority of github repos is ruby and javascript of which the majority is most likely rails related. Lots of people also use it to host their private scripts and little tools, you don't have that on sourceforge where most of the big opensource apps are hosted. Maybe Rubyforge will suffer. Anyway, I like github a lot and appreciate the upgrade, but I don't think it will overshadow sourceforge anytime soon.