Womder if they've allowed for baddies? The current URL shorteners such as tinyurl are supposed to be able to detect bad URLs but personally I never click on such things as I'm never convinced of their security. It doesn't take much to set up a new exploit domain - there are at least hundreds per day at the moment!
Still, as I never intend to use "social" sites such as fb and twit it probably won't be a problem for me. :)