With the advent of Github as the Ruby Gem hosting platform of choice, you have to be specific when you use config.gem in you config/environment.rb file.
Recently, I noticed that my Rails application generated from a You've Got Rails template was choking on the rubyist-aasm library. Given the following configuration in config/environment.rb:
Which would yield the following errors initially discovered when running Rake:
no such file to load -- rubyist-aasm ... Missing these required gems: rubyist-aasm
The problem appears due to Github namespacing gems by prefixing the username to the Gem name. The solution is to specify the actual library name:
config.gem "rubyist-aasm", :lib => "aasm", :source => "http://gems.github.com"