I've been using github for a few days now, and finding it nice.
I typically develop and host on my own mercurial repositories, but it is nice to share and be more visible. I love the way the initial README is displayed beneath each repository. Something that makes it really easy to scan the project contents and get a feel for the purpose/history.
I'm not yet decided if I wish to mirror my repos, the git plugin for mercurial seems to die under Squeeze, so for the moment I'm unable to do so. But it might be an option for the future.
Anyway should you care I'm here.