I think that it varies by jurisdiction, but around here (California, Silicon Valley) the jury commissioners compile their lists from voter registrations and driver's licences. If somebody is getting jury summonses unusually often, it might be because their name is recorded slightly differently on the voter's and DMV records, and the computer that generates the summonses is treating them as if they are two people.
I always show up, but I do have very mixed emotions about getting a jury summons.
On one hand, it's kind of exciting, it gives me a real-life look inside the justice system, and I kind of like the feeling that I'm doing my duty as a citizen.
But it's a hassle too, a major inconvenience. Sitting for hours in that jury room, waiting to get called, is stultifyingly boring. Oftentimes they decide that they don't need any more jurors that day and cut everyone loose around noon, before we get sent to a courtroom. When I have been sent upstairs, I haven't actually been chosen for a jury, though I've come awfully close a couple of times. Luckily (or unluckily) one side or the other has used one of their peremptory challenges to reject me. (The fact that I used to work for that county's DA's office usually catches their attention.)
