I must admit, while he will probably make a great Doctor, that I'm a bit disheartened by this. And this is only due to Torchwood.
Now before I rant on, I know that all previous companions and Doctors have been on the show in some incarnation or another. But this guy's a different deal.
He was on one episode in Doctor Who (oh well, that's fine) but he was a major Character in Torchwood season 3. Seeing as Torchwood is a spinoff of Doctor Who and official Whovian universe canon, they are using the same actor from a major series in the same universe, to now portrait the Doctor? That's a stretch even for this series (which is saying alot).
I will look forward to see them adressing this, becuase otherwise it seems like they are completely ignoring Torchwood and all the canon in that series. And that would make me a very sad panda, as I enjoy that part of the Whovian universe too