nothing to do with being "cool". Github have created a great piece of management software to view and manage your git repositories. It's easy to use and that is why its popular not used because its popular. Git itself is popular because its easier to use than SVN and is decentralized which is very useful.
> Github have created a great piece of management software to view and manage your git repositories
Therein lies the problem, and why it's not a good collaboration space for everyone (as has been implied elsewhere in this thread). I won't use it simply because I dislike dealing with git, for example. Yes, it's a great tool if you want to use git. The mentality I've seen become more prevalent over the last year to two years, however, is that you must be on Github to "do open source right"--setting aside the obvious silliness of that, it does still exist in a lot of places.
If they supported hg with the same infrastructure, I'd consider switching off of bitbucket, but given the Github folks' public behaviors in the past, it wouldn't be a guarantee. I've been treated very well by Atlassian and don't think particularly highly of the Github guys.
