Here's an extension that's quite at home with Cleaner YouTube. Naked Twitter relieves your Twitter account's homepage of all the sidebar clutter. The only remaining links (profile, replies, direct messages and log out) are represented by small icons at the top of the page. Additionally, there are no pop-up hover tips or lists. Boy it looks nice.
It's certainly not for everyone. Like I said, the groups, lists, trending topics, etc. that typically populate the page are gone. If you use those things, don't install the plug-in. However, if you like the clean simplicity as I do, you should definitely check it out.
Speaking of YouTube, developer Jacob Bijani has released Naked YouTube as well. Much like Naked Twitter, Naked YouTube removes everything but your video.