It seems to me the Bitcoin-qt 'Sign Message' feature is a little harder to use than it should be.  Once all of the fields are filled in, it would be more convenient to output a block of text that contains all of the information that should be pasted in to a message.  Also a simple parser that expects this format should be put into the Verify Message side of things.  For example (taken from a PGP Signed message):

-----BEGIN BITCOIN SIGNED MESSAGE-----
Address:  1Bitcoinasdfasdfsadfsadfsadf

Because anyone can claim to be me. There's no validation of the user
name or email address when someone posts a comment. While I do try to
remove imposters, some may slip through. By signing my comments using
this technique, anyone can independently verify that I was the author of
the message by validating the signature.
-----BEGIN BITCOIN SIGNATURE-----
Version: Bitcoin-qt (1.0)

iD8DBQFFxqRFCMEe9B/8oqERAqA2AJ91Tx4RziVzY4eR4Ms4MFsKAMqOoQCgg7y6e5AJIRuLUIUikjNWQIW
-----END BITCOIN SIGNATURE-----


--E