UPDATE: Dumb HTTP has been disabled as of Sunday, June 12, 2011 at 2AM PST. If you'd like a little more time to transition, please contact support and we can temporarily enable support on a repository by repository basis.
UPDATE: We've extended the shutoff date to Sunday, June 12, 2011 to give people a bit more time.
Starting June 7th, 2011, GitHub will no longer support fetching over Git's "dumb" HTTP transport mechanism. This won't effect you unless you're running a git version prior to v1.6.6 and fetch using a http remote URL.
Based on our logs, less than 7% of all git HTTP clients are using the dumb HTTP transport today.
Git v1.6.6 (released January, 2010) added a "smart" HTTP transport that is superior to the old transport in every way. We added support for the smart transport on April 22, 2010. The "dumb" transport is overly chatty on the wire and requires exposing internal repository data, restricting our ability to store things efficiently on disk in some cases.
Please check that your git version is at least 1.6.6 and upgrade if necessary before June 5th:
Most Linux distributions have newer packages available in their stable repositories. Latest versions of Mac, Windows, and Java clients should also support the smart transport.
If you rely on git's dumb HTTP transport and feel you have no easy upgrade path, we want to hear from you: please open a support ticket.