This article is quite old.Time flies when you're having fun. I've been writing for my blog for a long time. Stuff changes fast, especially in the Ruby world. That's why I've put this warning on old posts. The article might still be valid, though.
I was browsing through the gem documentation today, and I found a command that I didn't know existed.
sudo gem cleanup
It removes old versions of your installed gems. You can of course specify the gems you'd like to cleanup.