People keep bringing that up, but that's missing the bigger picture: GitHub is more than just a git host, it's also a "social hub" where people can fork repos and offer changes back (pull requests), a passable bugtracker (issues), even wiki, and even web host (github.io).

Many people have warned that using these added-value features makes you dependent on GitHub (Linus Torvalds has a kernel mirror on GitHub, but for this reason refuses to use its other features). Migrating all that metadata is hard (is it even possible?).