I haven't even been on Twitter for a whole year, and my account has already taken on a life of its own. I don't think I've become as obsessive about keeping my Twitter page as organized as my email inbox, but its disarray somewhat scares me.
Thankfully I found this site on Techie Buzz which will actually help you clean out your Twitter account. You know all of those inactive accounts you follow? MyCleenr will whip up a list of the unused ones so you can instantly stop following them. They swear they won't store your Twitter username and password, so it should be fine. My advice with security issues like this is to have a unique Twitter password, so you aren't entering something that is also your online banking login info, email password, etc.