In Air Measurement Tech., Inc. v. Akin Gump, __ F.3d __ (Fed. CIr. 2007), the court held that district courts had subject matter jurisdiction over patent malpractice claims between nondiverse parties. The defendants had removed the case from state to federal court, contending that the suit "necessarily depends on a resolution of a substantial question of federal patent law" because the plaintiff, an aggrieved patentee had to establish that the claims were valid, infringed, and that but for the defendant's negligence, certain defenses under patent law would not have been available to accused infringers.
I've dealt with this issue in various contexts, and the answer deserves clarification from the Supreme Court. (Why, for example, did this appeal go to the CAFC? There's an interesting question there, alone! Do other appeals have to?) I'm hoping the Supremes take this one up, as it's an interesting question and one in need of a definitive answer.