So the President of the United States signed the Electronic Signatures in Global and National Commerce Act into law. And the White House released a little fact sheet about it. But as this Reuters article points out, "The law itself does nothing to create federal requirements or repositories for signatures. That will be left to the marketplace, as will the issue of creating security surrounding digital transactions."
...so it could be a while before we see digital signatures catch on.
After signing it in ink, the president signed the bill with a smartcard. His password: "Buddy", the name of his dog. Aren't you glad the password the U.S. president uses to sign bills is broadcast in national media?
Also note that the white house publications server has a much better addressing system for referencing documents than congress does.