At first pass, sending a a letter like the one quoted below seems the wrong way to get out of jury duty.
http://www.clusterflock.org/2009/05/leave-me-the-f__k-alone.html (emphasis mine)
"I, ERIK ANTHONY SLYE, being first duly sworn upon oath, depose and say that jury service would entail undue hardship on me and that I request to be excused from jury service for the following reasons:
Apparently you morons didn’t understand me the first time. I CANNOT take time off from work. I’m not putting my familys well being at stake to participate in this crap. I don’t believe in our “justice” system and I don’t want to have a goddamn thing to do with it. Jury duty is a complete waste of time. I would rather count the wrinkles on my dogs balls than sit on a jury. Get it through your thick skulls.
Leave me the F__k alone."
Then again, after meeting with the judge the man avoided a citation and was excused from jury duty. I am not sure the next guy would be as likely.
More at http://www.thesmokinggun.com/archive/years/2009/0430091jury1.html.