Twitter has just announced a change to their terms of service and in an effort to keep users in the know, sent out an email notification with links to the new ToS. This is impressive since most sites post new terms of service without ensuring that users know about potentially important changes.
The most significant inclusion within the new terms from Twitter is the distinction that users retain ownership of their tweets, even though Twitter can transmit, modify, and display them. Another item outlined in the new ToS is exactly what is forbidden on the micro-blogging site. Users are not allowed to spam other users, impersonate people, name squat, sell user names, post porn, or infringe on copyrights.
Twitter is also up front about their position on advertisements in the ToS. They still want to leave the door open if they ever decide to capitalize on the popularity of the site with ad placement. Also, they are still working on a set of user guidelines for their new application platform.