Here's a great, lengthy interview with Dan Harmon over at Den of Geek, where he talks Anomalisa, Eternal Sunshine, Charlie Kaufman, and Harmon's other work.
I’ve really never seen anything as well-written, considering the full picture, because the original medium was just the actors sitting on stools and the radio play, plus a Foley artist. And, as I sat down I thought, “Well, I’ve seen this done before, you know, modern takes on the old art form, live radio with a Foley artist.” But then Charlie Kaufman proceeded to—as he always does when you look back on his career—use that medium, limitations and all, to express something about the human condition that you could only express with that medium about identity, individuality, and our fetish for difference. And it was just mind-boggling.
So I’d always mention that was, like, the best thing I’d ever seen written in any written medium, period. So I think that was part of why Dino asked Charlie, “Are you doing anything with that ever and if not can we adapt it into a stop-motion film?”
[...] [I had a] conversation with him where he asked me a lot of questions about why it is I liked performing. When Charlie Kaufman’s asking you questions you immediately become terrified that he’s sizing you up. I felt much safer staying as far away from the process and from him as possible because what could I do but fuck it up? He needs no help. All he needs is a safe place to do his work uninterrupted. If you could provide that and then hide in a cabinet until he’s done, I think you’re doing a great thing for moviegoers. (Source)