I just found this article from last week about the show and several new cast members: Dichen Lachman and Alexa Havins Join <i>Torchwood</i>
I have to say, I'm pretty happy with this. I liked Alexa Havens on All My Children and Dichen was awesome on Dollhouse. So, that's two Americans (the other being Mekhi Phifer, who I'm less thrilled about) and one Australian in the cast now. There are spoilers in the article about the characters and how they figure into Torchwood, so beware! Michael Ausiello has clearly never seen the show - he refers to Eve Miles as "Eva."
For me - and many fans - Captain Jack and Gwen are the stars, so I hope Russell Davies and the people at Starz are sensitive to that and work the new members of Torchwood in well and don't let them take over.