Ajax, the reload-free web 2.0 basis, is all the hype now, well it actually has been the hype for some months now, it’s already common knowledge now and not using (or at least not knowing) it adds this reactionary taste to you.
So if you want to learn about it, here’s your chance now.
This tutorial goes from chapter 1 (Ajax Tutorial: What is it good for) over a nice 30secund tutorial on to language-specific implementations for example for ruby

The Ten Best Ajax Links: Tutorials, Examples, and History > My Gadget Bag > We do the Research, So You Don’t Have to.