They said every actor that was in LOTR would have an opportunity to be in one of these next two - assuming their character appears. Here's the quote: "Unequivocally, every single actor that originated a role in the Trilogy will be asked to participate and reprise it. If Health, availability or willigness become obstacles – and only in that case recasting would be considered."
They reconfirmed that Ian McKellen would reprise Gandalf, but that's the only one they said for sure.
Guillermo waxed eloquent on the subject of Smaug. It seems that visualizing him is the most appealing aspect of the movie for him. So, I imagine Smaug will be suitably awesome in every sense of the word. They also said the elves of Mirkwood will be different from those of Imladris, but that's all they would say on the subject.
Anyway, it all sounded fantastic and I can't wait. The whole transcript is on www.theonering.net here.