GitHub is much larger by traffic, but that doesn't mean we are going to abandon the million users we get every day and the 430,000 projects hosted at SourceForge. It's not a zero sum game. Some people like using GitHub's suite of tools, while also taking advantage of SourceForge mailing lists, project website hosting, detailed download statistics, and distribution/discovery capability. Our GitHub Sync Tool lets project owners use both with ease.
I agree. After Github recently locked my private repos and demanded payment to unlock them, with no option to simply make them public instead, I'm 10,000% supportive of getting new (or, in this case, refreshed) competitors in that space, whether I plan to use them or not.