How reliable is eyewitness identification testimony?

According to the Boston Globe, the Massachusetts Supreme Judicial Court is scheduled to consider a series of cases next month involving the reliability of eyewitness identification testimony. Developments in psychological research -- and some DNA exonerations -- have caused some to reflect on the reliance that courts place on eyewitness ID testimony. Should jurors be given a special instruction regarding the potential flaws in such testimony? May the defense present expert testimony casting doubt on the general reliability of eyewitness identification? Courts are going to have to confront and address these questions sooner rather than later.