If you're a Mac user, you might want to take a look at Snagit, Tech-Smith's answer to Skitch, which I've been using for a couple of years.
They're beta-testing, so it's free...but don't expect it to work seamlessly!
Both programs allow you to take a screen capture, and then add text, arrows, etc., making them great for tutorials. Snagit has been available for Windows users for quite a while (my Mom loves it).
Here's the question, though: Skitch is free, so why would anyone pay for Snagit, once it's out of beta? TechSmith will really have to load on the features!
I like beta-testing (it makes me feel so cutting edge!), so I'll definitely take a look at it. And TechSmith is a fabulous company; I use Camtasia and love it, though, again, it's new and not as feature-rich as the Windows version. Oh, well!