http://www.saccourt.com/jury/general/general.asp#4
"What If A Juror Does Not Report as Instructed
Every resident of Sacramento County who is qualified to serve and who does not have a legal hardship or excuse must appear for jury service when summoned. Willful failure to appear is contempt of court. Contempt of court is punishable by fine of up to $1500.00 and/or five days in the county jail."
http://www.calbar.ca.gov/calba.../Serving-on-a-Jury.pdf
"If I receive a summons for jury
duty, do I have to respond?
Yes. For the system to work, citizens must
respond when summoned for jury service. Even if
you may not qualify for service, you must respond
to the summons. If you do not, you could be held in
contempt of court and be fined and/or sent to jail.
If you cannot serve on the summons date,
however, you may ask for one postponement to a
more convenient time. (Read the summons from
your particular court to find out how to respond in
your county.)"
http://www.courtinfo.ca.gov/jury/basics.htm#excuse
"Failure to Appear
If you are qualified and you have not been excused or had your service postponed, you must report for jury service. You may only have to call on the phone or check a Web site to find out if you should report for jury service. Any person who fails to respond may be fined up to $1,500. Jail time in addition to the fine is also possible. Carefully follow the instructions on the summons and contact the court if you need help."
Don't bullshit yourself by thinking they won't do anything. The judges take this very serious, and are prone to issue bench warrants for those who fail to appear.
This past March, I had to spend a couple of days doing court reports for my Business Law class.
Twice during those 2 days, the judge issued bench warrants for people who didn't appear and hadn't called in to postpone their duty.
In one case, this was the 2nd time the personhad skipped jury duty, and the judge ordered the Bailiff to call the Sheriff's office (the bailiff's are Sheriff's deputies) and have a car sent to pick up the missing juror.

I don't know if they ever found him or not, but I certainly wouldn't want to be that fellow.
Skipping jury duty is considered to be contempt of court...