Follow the interesting/appropriate links from http://en.wikipedia.org/wiki/Jury#United_States The details vary by jurisdiction.
As a member of a jury pool of 100, I was lectured at length by the judge on the definition of felony and felon. When he asked the members of the pool that might be felons to speak privately to him, fully 80% by count of the pool of a hundred lined up. That was very educational!
I was empaneled, even though I was an active gun rights and law and order advocate, and sat on a repeat DUI/DWI by a stereotypical used-car salesman.