I took part in an interview for the same position here in Austin. It did not take four hours, but they do divide the interviewers up, and when I did it, they took 5 of us at a time. The other group must have been there for close to four, but you're only interviewing for an hour or so, including everybody else. It was about 3 weeks ago, and I still haven't heard from them, so I'm assuming I didn't get the job. I was applying for it more temporary than I think they were looking for, so I'm not surprised.
I wish the questions allowed them to get to know you. They were pretty stupid questions, and had nothing to do (well, only indirectly), with the work they're asking you. They were questions like, "Describe a time when you had to work with someone slower than you." and "Describe a time when you did work that wasn't asked of you." I thought it was a really poor format, but then again, what can you do? It must work for them. They do give you a time to ask questions, and they go over the benefits package, and work expected of you.