Matt Smith is staying on as the Doctor at least through 2013, Kasterborous reports. It's speculated that Smith is negotiating a higher salary in a new contract for the series, and 2013 is Doctor Who's fiftieth anniversary.
Someone credited in the piece as "shadowy insider" had this to say:
“The current team believe that Matt is the person to continue taking the show forward over the next few years and want to avoid the prospect of fans having to get used to yet another actor in the role in the near future.”
This is fine with me as I have thoroughly enjoyed Smith's take on the character and can't wait to see how it will be refined over a long term. The show returns for a Christmas special that will air in the UK on Christmas Day followed by a full season a little later in 2011. This promotional image for the special was released recently: