I got a letter about two months ago or so asking me to fill out a short questionnaire because I may be called for a Coroner's Jury. I've never been called for regular jury duty, and as of yet they haven't actually called me for the Coroner's Jury, just let me know I'm on the list. My understanding is that it's similar to a grand jury, except you review strictly cases where death is involved, and you verify the coroner's findings, or suggest otherwise.
Doesn't really answer your question about when and if though, sorry.
BTW - One of my pet peeves is people who claim to be patriotic, or have pride in their nation, but try to get out of jury duty. Seems hypocritical to me to claim the US is the best place to be, but then try to work against one of the things that was set up to insure fairness in our society, no?