Cumberbatch is slated to play the voice of Smaug the Dragon for "Hobbit", a character who won't appear until the second film. He's also said he is doing movement and voice recording for another character which is currently nameless.
This production team alone has won 31 Oscars for their combined efforts on all three "Lord of the Rings" films. So, besides the amazing casting that has had my imagination nearly weeping for joy, it's no surprise to hear our lead Hobbit is "amazing". Thanks for the heads up though C-Batch!
Cumberbatch (on Left) with his "Sherlock" co-star, and "amazing" lead Hobbit, Martin Freeman