According to the New York Times, yesterday the US Supreme Court heard arguments in a case involving the Vienna Convention, which grants access by home country consular officials to people arrested in a foreign country. When I was a US consular officer in Brazil, I considered this the best guarantee against mistreatment, even possible torture, of arrested American citizens.
The virtue of this convention for Americans is not so much what it does for foreigners in the US, but the protections it affords Americans overseas. Similarly, the virtue of the Geneva Conventions is not so much the restrictions against torture that it places on American soldiers (although why the American government should embrace torture is beyond me), but rather that adhering to the Convention is a protection against torture for American soldiers captured by foreigners.
The report in the Times indicates that the Supreme Court may not find that any enforceable rights are created in US courts by the Vienna Convention, but the very idea that the issue made it to the Supreme Court, and that the Court may encourage local police and defense lawyers to notify the appropriate consuls is progress.
From the Supreme Court calendar, these cases, one from Oregon and one from Virginia, appear to be Sanchez-Llamas v. Oregon and Bustillo v. Johnson. A more legalistic report of the case is on the Northwestern University web site.