Top notch integration into Thunderbird Rated 5 out of 5 stars
Enigmail is a definitely a top-notch OpenPGP integration for Thunderbird. I installed the first iterations of this add-on when it first came out years ago but didn't have much need for it back then. It has gotten much more refined from what I can remember of the first versions. The smooth integration into Thunderbird makes it simple to encrypt and decrypt emails, once you understand the basics of OpenPGP.
I probably won't have too much need for Enigmail and OpenPGP, until the U.S. Congress decides it has the authority to snoop in my boring emails to family and friends without a lawful warrant. That is when Enigmail and OpenPGP will come into their own for me.
Recently, CNET ran a story about the Senate Judiciary committee tacking on riders to a bill which would have given the government access to peoples' emails without warrants. Luckily, that draft was publicly exposed and Sen. Patrick Leahy (D)-VT was forced to publicly proclaim that these riders wouldn't make it to the floor for a vote.
Google: "Leahy scuttles his warrantless e-mail surveillance bill" to read more about this most recent attempt by Congress to abrogate your privacy rights.