ERROR: While executing gem ... (Gem::RemoteFetcher::FetchError) bad response Moved Permanently 301 (http://gems.rubyforge.org/latest_specs.4.8)
gem sources -a http://rubygems.org/ gem sources -r http://gems.rubyforge.org/
Looks like they weren’t kidding when they said to switch from rubyforge to rubygems.org (née gemcutter)!
[Edited to change "http://production.s3.rubygems.org/" to "http://rubygems.org/". Note that the trailing slash is significant!]