If I were going to predict where their first misstep will come, I'd go with Cars 2 which will be out in a couple years. (I'm not saying it will suck, just maybe not quite live up to expectations.)

They've only done one sequel before and hit a home run with Toy Story 2. But whereas Toy Story ended in such a way it pretty much invited a sequel, Cars concluded like they didn't really intend to revisit it again--right down to the epilogue montage showing what transpired after the main story ended. Sequels are always tough and the ones where they decide after the fact to make them are harder still. All I've seen on the story is that the cars will be "going international." If anyone can make it fly, Pixar can. But I wonder if there's enough fresh material there to live up to the original.