The LA Times’ John Horn, writes about previous Pixar employees who have now gone on to direct animated feature films at other studios.
Pinkava speaks highly of Pixar. "It’s a tremendous environment, a company based on everybody wanting to do great animation." But after "Ratatouille" he decided it was time to go. "I was never quite on the inside of Pixar — I was on the edge of the inner circle. But I have no complaints, really. None."
says the article. And all the other artists speak very highly of Pixar too. It’s worth the read of the entire article.