I always show up unless I will actually be out of down the days of required service - because my experience is sometimes I just show up for the two days and never get selected for a jury and that fulfills my duty for the next 2 years. The one time I was selected for voir dire and was initially chosen I spoke with both attorneys and informed them I had a non refundable ticket to travel before the estimated finish of the case and they excused me - I think neither was happy about the prospect of having a disgruntled juror on the panel.