This is what happened when I want to install rmagick gem.

username@username-desktop:~$ sudo gem install rmagick
Bulk updating Gem source index for: http://gems.rubyforge.org/
ERROR:  could not find rmagick locally or in a repository

What the hell…
After some googling I found that RubGems 1.1.x is buggy and and update to RubyGems 1.2 is necessary.
To learn your RubyGems version:

username@username-desktop:~$ gem -v
1.1.0

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