I was chosen once - had to sit in a room with about 40-50 others for I think it was at least 6 or 7 hours a day for a week.
You waited until you were either called to be on a jury, or the cases for the day were over, at which point they'd come tell you that you were free to go, and make sure to be back the following day.
I think I was called on the 2nd to last day to serve as an alternate juror (in case someone got sick, run over by a car, etc.)
We were given pads of paper and a pen to write down notes about the facts and evidence given, and at the end of each session, the guards took the notes for safekeeping.
Our trial lasted 3 days, and it was deadly dull. At the end, since the 2 alternates were just that, we weren't allowed in final deliberations, and because we exceeded the original week, our service was considered fulfilled. (Had it been at the beginning of the week, we would've had to go back into the jury pool to possibly be picked again.)
There ya go, real life story about how dreary and boring the process is, although I'm glad I did it - it was a good experience.