Glenn Fleishman of The Seattle Times put together a nice little primer on PGP that I think all you paranoid types should take a look at.
Pretty Good Privacy (PGP) is the commercial version of the distribution originally released over at MIT (no longer in distribution). It plugs into your email and instant messaging clients, and can encrypt your choice of transmissions. For those on the other side of your communications, it means you can still sign (for authenticity) your emails, and they can read them without PGP. For those you deal with that have the program, you encode messages with a very very high degree of confidence they will not be read by the wrong folks, using standard public-key encryption methodologies.
What I think is the best feature of PGP is its virtual disk function. Create a space on your hard drive, encrypt it with a long string, and load your files into it. When mounted, you have access to those files just like any drive/folder on your machine. Unmount, and it becomes a bunch of garbage to anyone sneaking around.
Now, for the fair warning…
You scumbags out there taking violate pictures of the innocent and other such disgusting crap are not protected by the fair use of PGP. A Minnesota court recently ruled that the existence of the software on a scumbag’s machine was evidence of criminal intent.
But for those of us who use the program to secure valuable data (like images of bank and credit card statements, legal documents, and sensitive client files), particularly on easy-to-pick-up-and-walk-out-the-door-with laptops, it is a worthy piece of code.