GitHub has great popular momentum and it doesn't appear to be letting up - although each of these hosting sites has had its day in the sun.
We switched away from java.net to GH for our code repository and Google Code for documentation, releases, and issue tracking, as we felt the tools on GC were better (when we evaluated, maybe 12+ months ago). A big advantage of GH is that people can "fork" your code with no effort at all, meaning they can play with a copy of it in a public or private repository without asking your permission, and when they want to give back they can just point you at some changesets. This is really Git that allows that, but GH seems to make this fairly comfortable by providing UI tools for forking, for tracking branches, etc. I follow a fairly randomly selected bunch of tech geeks and programmers on Twitter and my sense is that GH has the lion's share of the action these days. Basically all links for most new projects that I'm made aware of are popping up on GH HTH Patrick
