Here's an article from today's news, "Dallas' Most Famous Person Shows Up For Jury Duty" that reported that George Bush Sr. just reported for a Dallas jury. Apparently, ex-presidents could get called.
Would they have an easier time getting out of it than most of us? Probably, but it's good PR for them to do their civic duty. The article did say that he had to be accompanied by a security detail, so it's certainly a bigger deal than when the rest of us just have to worry about finding a parking place in a big city.
According to the report, he was quite friendly and had his picture taken with lots of people in the courthouse.
Also, here's more information about the importance of jury service.