I ran into this problem today when trying to update my ruby gems on a fresh OSX 10.5 machine for testing:

Updating RubyGems…
ERROR: While executing gem … (Gem::RemoteSourceException)
HTTP Response 302 fetching http://gems.rubyforge.org/yaml


After a little googling I saw where gems were stored on S3 so I just added the —source option and that worked. Here is the command for posterity.

gem update —system —source http://production.s3.rubygems.org/