Jury Duty freakin Rocks! I got out of work for two days (I'm salary so I get paid either way.)
The first day was for selection, you will sit there for a few hours and go through the selection process. If you get choosen then you get to come back whenever the hearing begins. For me it was the next day. We showed up at 8:30, they had donuts and stuff setup for us. About 10:00 they came in and told us that both of the prosecuting attorneys were sick and the case was declared a mistrial. We were out of there by 10:30. They paid us $80 for showing up! and I had the rest of the day off.
They will give you a note that you present to your employer. Like GT said, your work can't do anything about Jury duty.