I just installed the GPGTools on my Mac running Snow Leopard this morning. All of the Services seem to be working exactly as predicted, but unfortunately GPGMail seems to be having difficulties.

So far, I have received a total of three PGP-encrypted emails. Two of them were decrypted flawlessly, but GPGMail refused to decrypt the third one. I typed in my password, clicked "OK", but nothing happened. All three messages were sent by the same sender, and encrypted using the same key. The stubborn third message was decrypted easily using the decryption Service, so this problem was specific to GPGMail.

Also, I tried sending myself a test email, which was both signed by myself, and encrypted to myself. Yet again, I could easily decrypt it using the Service, but no luck getting GPGMail to decrypt: this time, without even asking me for a password, it says: "Message has been encrypted but not signed. Its authenticity cannot be proved."

P.S. Another odd -- but not really problematic -- behavior that I noticed, was that the digital signature of the message I sent to myself was verified using the verification Service, before it was even decrypted. I just highlighted the PGP-encrypted message, clicked Verify, and it confirmed the signature. But, for all of the messages that were sent to me by another person, I had to first Decrypt and then Verify, or else the verification would fail, with the error: "No signatures found within the selection." I'm wondering, which is the "correct" behavior?