I looked around for some export functionality for github but I got a lot of posts complaining it wasn't there. Since I hate applications that take your data and refuse to let you remove it, I was disappointed by this news but further inspection showed that although there might be no "export from github" button, there's an API that more than has it covered. The API returns JSON which is easy to work with from many programming languages, and is perhaps even more powerful and flexible than the simple export I initially expected, so here are some examples.
I'm deeply involved with an open source development project (joind.in, the event feedback site) and we recently made the decision to move our issue tracking away from GitHub (because it's awful and meets none of the requirements for a bug tracker, but that's a post for another day). In order to make this happen more smoothly, we wanted to migrate our open issues from github (to JIRA Studio, since Atlassian generously provides accounts here for worthy open source projects - thanks Atlassian!).