Joseph:
1. While frum Jews rarely sue each other in a non-Jewish court, it does happen when a third party is involved (e.g. the insurance company in a state with “fault” insurance, or in bankruptcy when a third party assumes a claim);
2. The American rules of evidence are very narrow, whereas in halacha the Beis Din can use any information at their disposal (we don’t have “exclusionary rules” as even when a type of evidence is not formally allowed the court can still consider it). On a jury, you are legally free to consider facts that are excluded – a good example is most jurors know that when a defendant “please the fifth” it is because he is guilty of something he doesn’t want the jury to know about, and all the “curative” instructions from the judge don’t help.
3. If frum Jews avoid serving on juries, you can count on people we don’t like taking our places. It similar to voting – you can argue against it, but the bottom line is that’s its in our interest to serve as jurors.