Rubygems has plugins now! I've got an awesome one in the works for Apple's Dictionary.app coming soonish.
To see the gem plugins in action, try this:
% sudo gem update --system
% sudo gem install graph
% gem graph
Assuming you have graphviz's dot somewhere in your path, you'll wind up with a dot file and a png file of your rubygem state. Here's mine:
(click to view full size)
You can read more about rubygems plugins by reading the doco for Gem and Gem::CommandManager.
I really like the graphing functionality. It's a great way to learn about the gems other gems are built upon. After looking at my graph, I've added launchy, daemons, and directory_watcher to my list of gems to check out.
Keep up the great work!