I suspect that this is why people tend to understand when GitHub goes down, and this allows them to be more open. All (or nearly all) of GitHub's users are tech-savvy, so we tend to understand the problems.
Definitely the important part. Linus Torvalds once joked: "Only wimps use tape backup: real men just upload their important stuff on ftp, and let the rest of the world mirror it." Distributed SCMs like git are a great way to
But GitHub's main value over something like, say, gitosis, is all of the metadata. This stuff is mainly useful to github users. Projects you're watching, pull requests, bug reports, fun (if only of dubious general use) graphs. That stuff doesn't come across the wire with the individual repos. The big (in terms of bytes) part, the "events" table, is helpful for keeping up with people and projects (if sometimes noisy). I use the RSS feed of that, though, so I didn't even notice the interruption until I heard about it here.
