I've been playing around with Mozilla labs ubiquity plug in in recent weeks. It's still in beta, and far from fully featured, but even so it's quite impressive.
Tonight I was reading comments on a boing boing post where a few of the commenters had used ROT13 to obscure spoilers. There are plenty of good sites to do the conversion for you (I'm too old/lazy to do that sort of thing in my head these days) but I thought to myself that this would be a perfect for for a ubiquity command.
You can check out my notes here. Even if you've no interest in my almost embarrassingly trivial utility, check out ubiquity for it's own sake. If you're a power web-user, you won't regret it.