GitHub has been on & off all day today, and at first one would imagine that that would cause a gigantic PITA for developers, and that productivity in all places 'silicon' (valley, fen, glen, roundabout, savannah, desert, glacier,...) would plummet.
However, since GitHub uses git, and git is a DVCS, whilst users will have lost all the shiny unicorns that GH provides, they could, if their work really mattered, have simply pushed their repository to another hosted git service - like Codebase, BitBucket, Assembla, ..., and then carried on as normal. A little bit of coordination required to get teammates the new repo URL, and they'd be back online in minutes.
Or simply continued working locally, and committing, until GH gets back online.
I've often done the reverse - I have private repos in BitBucket (free!) which I have periodically pushed to GH in order to take advantage of some of the branch visualisations.
Try doing that with TFS or SVN.