I am probably the target audience :-) Basically, to use GPG, you need to understand how it works. To understand that, you need to be quite technical and also willing to spend several days reading and thinking about what the implications are.

I uses GPG for encrypting files for the most part. I also use it for some of the situations where you might use ssh -- not because it's a good idea, but rather because I wanted to learn how to do it.

My main use for GPG, though, is for distributed authentication. PGP's web of trust is quite useful if you know how to use it. Very few people use it, because they don't know how -- and also PGP's protocol makes it very difficult to understand how to use it. On top of that, GPG's UI makes it even more difficult to use. But if you can wade through all that, it's fine :-)

The main scenarios where I think WoT is useful is where you have a historical relationship with someone and that relationship is more important that their actual identity. For example, maybe you exchange haikus with some guy that you don't know. They claim to to be Matsuo Basho, which you think is a bit fishy, but you just want to ensure that all of these haikus are from the same person claiming to be Matsuo Basho (and not someone pretending to be the person pretending to be Basho). Now if your Basho pretender wants to introduce you to their painter friend Claude Monet, you don't actually care if it's actually Claude Monet (you'd best be suspicious). However, when someone claiming to be Claude Monet contacts you, you want to be sure it's the same Claude Monet that your friend Basho recommended to you.

These are the kinds of scenarios where PGP implementations (like GPG) are pretty much the only way. You can do it by hand, but using GPG is very slightly easier. A more realistic scenario might be that someone is giving you requirements for some project and they want to delegate some of the specification duties to someone else on their team. You are a remote contractor and have never met any of the people involved. You are satisfied that your original specifier is valid because they keep paying your invoices, but you want to be sure that any other people you interact with are authorised to deal with you.

I can think of some uses:

* Some package managers use it to sign binary packages. (Think apt-get)

* I personally use it in shell scripts to avoid storing some secrets in the clear on disk. (Use case similar to ssh-agent)