I imagine everyone who cares already knows that David Tennant will (sadness!) be leaving the show in early 2010 after a series of four specials to be broadcast this year. (Plus the 2008 Christmas special, which has already aired in the UK but not in the US.)
I'm dubious about Smith, especially after watching his nearly content-free interview with the BBC about being picked. However, I was dubious about Christopher Eccleston as the ninth Doctor, but was won over quickly; and then I was very dubious about Tennant when he took over--and he may well now be my favorite Doctor. So I'm willing to give the people in charge the benefit of the doubt.
I had been thinking that the day was ever-faster approaching when they would have to decide what to do after number twelve, but actually it turns out that (a) a Time Lord gets thirteen bodies total (twelve regenerations, not twelve bodies), and (b) there's a suggestion that that limit may have been a social limit rather than a physical one. The BBC's series 4 plot and continuity FAQ (that page contains spoilers for the latest season) says, in response to the question "How many regenerations does the Doctor have?": "Now that his people are gone, who knows? Time Lords used to have 13 lives."