I'm not convinced that there is a dress code at jury duty anymore, at least not in Philly. At the minimum, I don't wear jeans-----but then I regret it seeing 90% of the dudes wearing jeans; valuable breaking-in time lost. The system is broke-----dress accordingly.
In NYC, only nudity is prohibited. As you can imagine, the range of dress varies.
I would offer that, because a jury is charged with a solemn duty, even in the context of civil litigation, but will be sitting in one location for long periods of time with unpredictable climate control, one ought to dress a) as if a attending an official funtion (business casual at worse) and b) in the more comfortable version of those clothes. I would wear treousers, sportscoat, shirt, tie, and comfortable shoes. If in a summer environment, be prepared for possibility that courthouse A/C may not be very good. Take lots of reading material.
I always get called in the dead of summer as well in NYC.
First day of my first time, I showed up in a seersucker suit with a bowtie. I must have looked like a freak when compared with my peers. Ever since then I have worn whatever was comfortable, but not shorts. I have been called at least 3 times and have never even made it to voir dire.
In terms of selection likelihood, your answers to voir dire questions and overall demeanor are more important than what you are wearing, unless you go completely over the top. I've seen reasonably well-dressed people who sounded like nut cases when answering voir dire and got bounced, conversely I've seen impaneled jurors who looked like they dressed by crawling through a dirty laundry hamper and keeping what stuck to them, but sounded well-reasoned and thoughtful in answering questions. So wear whatever makes you comfortable sitting around for eight hours.
I'm often surprised at the choices attorneys make in voir dire, but the general rule is that the more extreme your answers are, the more likely someone will bounce you.
Actually - when we had this discussion before and I asked the same question, probably lost in the great crash, I think the suggestion was - if you don't want to get picked, wear a suit and tie - but if you do want to serve, wear a pair of khakis and a shirt.
It seemed counterintuitive to me, but the lawyers apparently don't want someone who looks too much like a lawyer or a business person. Criminal case, they think you'll be too law-and-order; civil case, wearing a suit signifies that you'll favor the large corporation or organization.
Of course, the important part is - I wore a nice suit and tie and was not picked for jury duty.