I'll say it's probably closer to 3 minutes for most -- how can you be a developer today and not have at least touched github once or twice?
That, and the fact that GitHub is a closed source backend under control of a corporation that's accountable to no one.
And I have no problem with a project not wanting to use github for this reason either - everyone is free to roll their own, or use something else, but the point stands that SF isn't exactly a better alternative for those reasons and most small projects should just end up on github because that's where a lot of OSS development has coalesced anyway and at least github has a been a decent steward providing free OSS project hosting.
1. "and the fact that GitHub is a closed source backend under control of a corporation that's accountable to no one"