How hard is it for people to switch, if they want/have to? They might be dependent on GitHub issues. That might be preventable by using some issue tracker that

How hard is it for people to switch, if they want/have to? They might be dependent on GitHub issues. That might be preventable by using some issue tracker that can actually be put under git (like Ditz), though I guess it makes collaboration with non-owners of the repository more difficult. Other than network effect, what else is it that binds people to GitHub?