I have been called four times (2 different counties) but have never actually served on a jury, or even been interviewed.
First time, I had to go sit in the jury pool room every day for a week. They had us fill out a questionnaire the first day, then as they seated juries, they'd come in and call out which people needed to go be interviewed. Once they sat all the juries they needed that day, the rest of us were excused till the next day. One of the questions on the questionnaire was whether you or any of your family members worked in law enforcement. My dad is a retired police officer, so I think that might have gotten me knocked out of the running right away, but not enough for them to tell me I didn't have to come back.
Another time, I got the summons right before we left to adopt our daughter. I was going to be gone for a while (including the start date of my jury duty). I sent in the request to be excused but it clearly said that. you are NOT excused until they tell you you're excused. I didn't hear anything -- I ended up calling the court the day before we left and he granted my excuse over the phone.
The other two times, the instructions said that you were supposed to call a number after 5pm the night before you were supposed to appear. They would tell you whether you needed to report the next day or not. I called the number and every night it said that potential jurors did NOT need to appear, so I never even set foot in the courthouse.