The 11h Doctor has just been revealed on BBC1 at 5.59 today (about 20 minutes ago). Taking over from David Tennant will be Matt Smith, a little-known actor in his mid-twenties.
The BBC will be showing an interview with Matt at http://www.bbc.co.uk/doctorwho/
The reveal program, Doctor Who Confidential showed some interview footage with Matt where he mentioned that after being given the part he was just pacing around for three days thinking of it. He also talked of watching Doctor Who with his flatmates after being chosen, and having to keep it secret that he would be the next one. He has 6 months to prepare before filming starts.
He's the youngest ever choice for the 900-plus year old Doctor. From the brief interview clips, I think he can do it though. Congratulations to Matt.