You may have seen this message from "gem install" before:
Then when you run "gem install rails" five minutes later, it installs just fine. This was due to the way we were rebuilding the gem index on RubyForge - we were doing it "in place", so that the current index would be overwritten and then populated over the course of the build. These take a fair while - 10 minutes or so - and during that time the index was essentially empty. Booooo.
Well, no longer. Eric Hodel has twiddled the gem index builder to build it in a temporary directory and then move it in place. So those gem index outages should be a thing of the past. Thanks Eric!