Ajax - what gives?

Ajax is popping up all over. This, in case you are one of the multitude that doesn't know or care, is a technology that allows a page to change without refreshing the whole of itself. So for example, you might have a checkbox that saves the page automatically when you check it, rather than having to press a separate button. It's a clever little idea that uses Javascript. So far, so good.

( If you don't care, don't click... )