Ownership—Twitter is allowed to “use, copy, reproduce, process, adapt, modify, publish, transmit, display and distribute” your tweets because that’s what we do. However, they are your tweets and they belong to you.
From: "Twitter Tweaks Terms Of Service, “Your Tweets Belong To You”
God bless you Twitter. #getupandmove :) Now, will we see people begin to copyright their Twitter accounts and tweetnames?