For those of you not familiar with encryption, the basic idea is that you're communicating in a secret code. When someone sends you a message, they use your public key to encrypt (lock) it. Then, only your private key can decrypt (unlock) it - nobody else can read it.
PGP isn't totally uncrackable, but it's pretty close (with a 2048-bit key, cracking it by brute force on today's average computers would take longer than the known life of the universe). It's not "stake your life on it" level of privacy, because a) it's possible that someone's cracked it in another way and we don't know, and b) in 10 years time, a brute-force approach to our currently encrypted stuff will be trivial (especially with DNA computers and other massively parrallel algorithms). But in practice, that doesn't matter now - encryption between two people using PGP is (for all intents and purposes) private.
I like the idea of using encryption because it jives with our perception of how we see the world. When we write emails, we act like it's a private conversation; but that's simply not true. Anyone along the way -- from ISPs to random people sniffing packets on a network -- can read your email, and it probably happens more than you think. This is especially true in corporate environments where the management has not only the capability but the legal right to read anything you write on their computers. With encryption, though, it really is the case that (as we all assume) only the people involved in the conversation can read the message. Our assumptions of privacy become a reality.
Anybody else out there use PGP encryption? Wanna swap keys? Here's mine.
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1.4.3 (MingW32)
-----END PGP PUBLIC KEY BLOCK-----