Gem building has been disabled since the move to Rackspace. This was because the system had to be rewritten to work with the new architecture and we had to provision an entirely new VM for the sandboxed gem building – things we didn’t want holding up the move.
Well, it’s been a week and we’ve decided to not bring back the gem builder. It was a fun experiment but Jeweler and Gemcutter combined make it ridiculously simple to publish a gem. The gem builder use case (fork a project, make a change, publish a gem, install it) is now easier than ever using these tools.
As for namespace support, Gemcutter is working on it. We encourage you to help!
We will continue to serve old gems at http://gems.github.com/ for at least one year. Thanks.