Criminal defense attorneys should ask in all initial interviews the birthplace of the defendant. Don't fall into the trap of doing this only in cases in which the client doesn't "look" like an American citizen.
For more Padilla Practice tips see:
Practice Advisory: Duty of Criminal Defense Counsel Representing an Immigrant Defendant after Padilla v. Kentucky (April 9, 2010) (237K PDF). This practice advisory, prepared by the Immigration Defense Project for the Defending Immigrants Partnership, provides initial guidance on the duty of criminal defense counsel representing an immigrant defendant after the Supreme Court's Sixth Amendment right to counsel decision in Padilla v. Kentucky (U.S. March 31, 2010). In this decision, the Court held that, in light of the severity of deportation and the reality that immigration consequences of criminal convictions are inextricably linked to the criminal proceedings, the Sixth Amendment requires defense counsel to provide affirmative, competent advice to a noncitizen defendant regarding the immigration consequences of a guilty plea, and, absent such advice, a noncitizen may raise a claim of ineffective assistance of counsel.