For Linux there's Seahorse, the Gnome app for managing PGP and SSH Keys. It comes installed by default on Ubuntu. Generating a key and synchronizing it with a key server couldn't be more painless.

For email clients, you can use Thunderbird or Evolution, both of which can handle PGP. There's also a new Chrome/Firefox extension that brings PGP to Webmail interfaces, such as GMail: http://www.mailvelope.com/ ... because of a Firefox limitation, it's kind of slow on Firefox right now, but should get fixed in 27 and it also lacks advanced features (e.g. PGP Mime, or syncing with key servers), but those features are coming.

Linux in general have the best security related tools. Ubuntu's graphical installer for example gives you the option to encrypt either your $HOME directory or your entire hard-drive (with dmcrypt). When formatting an USB Drive, you also have the option to encrypt it. And if you synchronize your files on DropBox or Google Drive, you can quickly create an encrypted folder by means of Encfs / gnome-encfs. And personally, I went full on with encryption. My hard-drive, my USB drives, my Dropbox, my Google Drive storage, all encrypted. I also link to my PGP public key in my email signature, which is cool, as my personal website serves links only through HTTPS.

Yeah it looks good in theory, until you start really using gpg and promote it amongst friends and contacts...

I actually don't really understand the differences between PGP/INLINE and PGP/MIME but it has given me headaches, because some clients don't support both.

Evolution's devs refused to support anything other than PGP/MIME for a long time (seems to be fixed now):

http://mozdev.org/pipermail/enigmail/2010-July/012617.html

K9 cannot read PGP/MIME https://code.google.com/p/k9mail/issues/detail?id=5864

The Thunderbird-with-PGP experience on Windows is atrocious, absolutely disgraceful.

Here's what I blogged after trying it a few months ago:

I suspect the way most people on Windows will use PGP is by downloading GPG4Win and Enigmail. The fact that this is two separate things to install is a showstopper for a lot of people. Installation of Engimail requires right clicking on a link to save it, then locating the file in Windows Explorer and dragging it into an open Thunderbird window. I can do that and you can do that, but it's arcane wizardry for a significant portion of the population.

Also, the GPG installer appears to randomly crash under certain circumstances on Windows 8.

That's just installation. Then you have to get people to generate a key using a password that's different from the one they use to login to their email server. I suspect most users would have a difficult time using the GPG interface; it's very reminiscent of desktop Linux applications a decade ago.

There's more, but it's too long for here: http://jamesgecko.com/everyone-should-use-pgp-but-its-kinda-...

I use it wherever I can, but encryption is something that requires the participation of all communicants. The only option for an unwilling or unable participant is to be excluded from the mail completely and contacted in a separate channel (preferably Real Life). This, combined with the fact that encryption requires effort, makes it very, very hard to propagate.

Encryption for mail will remain practically zero until someone implements an extremely simple, integrated user experience. It's one of those things no normal person will acquire unless you ship it with Windows and make it totally transparent.

gpgtools is great. It integrates very nicely with Mail.app.

Any suggestions for what to do on an mobile device to pair with desktop mail?

I was just starting out with PGP today - and found iPGMail to be useful on iOS.