According to an 8/8/08 article in the New York Times Business Section (click here for PDF download), the answer is settle, at least if you are the plaintiff. A study of civil lawsuits showed that 60% of the time plaintiffs end up losing on average $43,000 if they proceed to trial after rejecting a settlement offer. Defendants made the wrong decision less often (21% of the time), but when they did get it wrong the cost was much greater: $1.1 million.
Ideally you will never be involved in a lawsuit; but if you are you may want to keep this data in mind as you contemplate settlement versus trial options.