The National Immigration Project of the National Lawyer’s Guild has recently issued a Practice Advisory on the retroactive applicability of Padilla v. Kentucky. It concludes that Padilla should be applied retroactively by the lower courts because it does NOT create a new rule of criminal constitutional law. The practice advisory can be downloaded here.
Also, a recent decision from Judge Seybert in the Eastern District of New York touches upon but does not decide the issue of retroactive applicability of Padilla — she assumes for the sake of argument that it does apply retroactively and then goes on to reject his Padilla claim on the merits. The case is United States v. Obonaga (E.D.N.Y. June 24, 2010) and can be accessed via Google Scholar here.