United States v. Castillo, ___ F.3d ___ (9th Cir. Sept. 22, 2006) (appeal from conviction by guilty plea for being an illegal alien in possession of a firearm dismissed where defendant's entry of an unconditional guilty plea deprived the appeals court of jurisdiction to consider his pre-plea constitutional claims, and that jurisdictional defect is not waivable by the government).
http://caselaw.lp.findlaw.com/data2/circs/9th/0530401p.pdf