I've worried about jury duty for a while. Recently my friend got a summons in the mail. It came three days after she mailed in her voter's registration card, so obviously that's what triggered jury duty for her. They do use voter registrations list to decide on who to summon, after all. But not exclusively.
If I'm ever called in I'll try my hardest to get a doctor's note to be excused. Of course, one look into some of my documented history and I'm certain that no jury would want me anyway.
I wouldn't advise anyone skipping out on jury duty without letting the courts know. It seems like a small offense, but we all know that the legal system has a penchant for blowing things out of proportion. People have been arrested for continuously dodging jury duty, and I have no doubt that they'd love to fine you a large sum of money for doing it too.