Synecdoche, New York was screened as part of American Cinematheque's Charlie Kaufman restrospective, and Charlie gave a Q&A after the film. Here's a short clip where he talks about working with Philip Seymour Hoffman. He mentions fearing that Hoffman might back out of the project, the producers' initial dislike of the film's ending, and Hoffman's fine-grain understanding of the film.

See also this Q&A with Charlie and Catherine Keener at the Malkovich screening, and this one with Charlie and Spike after Adaptation.