One problem with the idea of court screening of scientific experts under Daubert is that some judges simply don't have the scientific training not to be snowed by the same junk science that has the risk of unfairly snowing jurors. (I saw this in a class action settlement where a junk-economics expert waved his hands and gave an ipse dixit that requiring defendants to sell larger gallons of gas would mean that class members would get millions of dollars of free gasoline in the future. Oy.)
Attorney Nathan Schachtman (via Childs) finds a very good example in the Avandia MDL, which independently raises the question why judges who don't understand science or questions of statistics are assigned to MDLs where science and questions of statistics are going to be decisive factors. [more from Schactman]
Schactman also has an interesting post about the misuse of historians as expert witnesses.