In Tweeting about Twitter's Terms Dave Winer writes:
You can't be half in and half out. Either you connect to Twitter, and they own you and your users, or you don't connect to Twitter.
So we can't play with Twitter, but the other way around Twitter can't play with us. At some point in the future rssCloud based microblogging clients will take off and Twitter will have to change their terms of service to allow us to let them play with us. At that point we won't care anymore.