[ken]

GitHub wikis are just git repos themselves, and I clone mine. It's easier to edit them locally, too.

As for issues, I've suggested to GitHub that they make them available via git, and they said simply "I have passed your suggestion on to the team to consider adding the ability to clone Issues". I don't think they realize how nerve-wracking it is to put any data at all in GitHub issues. Even their recommended backup software is out of date and doesn't back up Issues completely.