The starring role in Doctor Who will pass from David Tennant to Matt Smith -- Doctor WHO?! indeed!! And what are they thinking over there in Cardiff, he's even younger than Tennant! At 26-years-old, he is the youngest actor to play the Doctor ever!
Interestingly, though, of the 30-odd "Matt Smith"s in the Internet Movie Database, this Smith is Number Eleven...!
Another reason he's perfect for the job? He's already lusted after Billie Piper! (He was "Tim" on episode six of Piper's "Diary of A Call Girl" series)
ETA: My new poll about Matt Smith is at http://www.sodahead.com/question/224077