Even though Peter Jackson is supposed to be directing the film, it might never get made because MGM is in a financial hold. Unless they get the money to fund the Hobbit, nothing is guaranteed.
One of the few things that is fully confirmed is that Ian McKellen would return as Gandalf. He's the first and only confirmed cast member....but that might not even be a guarantee anymore.
Talking on New Zealand's Good Morning show (via Bleeding Cool), McKellen emphasized that he's not under contract for the film, and maybe he'd rather get up to something else rather than constantly waiting around for MGM to pull itself together. Here is what he said.
"Well I’m not under contract and my time is running out and I’m enjoying working in the theatre and frankly, I would like to race after doing Waiting For Godot, get on with doing another play but we’ll have to see. I don’t give the producers the impression that I’m sitting waiting."
You can watch the video version of the interview below.
The Hobbit comes to theaters in 2012. I wouldn't count on it though.