I am assuming:

1. You are on OSX & using Gmail
2. You can live without being in Gmail web interface 100% of time
3. You don’t mail that much from iOS
4. You secretly hate Google and want to use their infrastructure as a dumb data pipe

I suspect many, many people hate Gmail interface (and maybe even the whole Google interface approach). That’s why Sparrow was doing rather well until it was “neutralized”. Anyways now that Sparrow is more or less finished, many people from the “native” camp are looking around for alternative mail client.

As if all that commotion was not enough I’ve recently started looking for a way to encrypt my mail messages. (NO! I am not paranoid. I am acting strange from that stuff that government is putting in our tap water to minimize chip implants rejection :))

Sparrow lack of ability in that area has led me to return to Gmail. To be honest doing mail that way is tolerable. As for encrypting, the only thing I could find was Mymail-Crypt for Gmail. It’s just barely enough. It’s rather tedious in practice (pass phrase is needed every time, signing is bugged, sometimes I was unable to decrypt the message for no apparent reason).

Since this plug-in was using GPGTools underneath it seemed logical to try out the “real stuff”.

GPGTools integration into OSX is superb. I was so not expecting this.

I had no hassle whatsoever. My messages are encrypted, I don’t even have to think about it. The only time I see what I am doing is when I glance over PGP message in Gmail. I wonder what Google parser thinks of it :)

You need five minutes to setup GPGTools (you need beta version if on Mountain Lion), generate your key pair, upload it to the key server and start using it in your mail correspondence.

Key server part is optional, but it eases distribution of your public key. For example this is my public key.

Conclusion

You should download the GPGTools suite and try it out. As for the Mail.app, at least you have a long term support for it.

Pros:

1. Feeling like a man
2. Keeping that nosy AdSense Gmail engine at bay
3. Being more secure

Cons:

1. Search on encrypted mails is not working
2. Gmail support is a bit shaky - Mymail-Crypt for Gmail(Chrome) is not that great
3. iOS devices support is questionable - this can also be a benefit, not being able to check your mail on iOS devices?