AJAX controls are cool, sometimes
I'm finally using the AJAX stuff in a project of mine, and I have to say that, for the most part, I'm impressed. The ton of stuff you have to drop into web.config is a little annoying, but there are some amazing tools in there.
I'm a little disappointed with the fact that I can't seem to make any of the stuff work right in a repeater. If there is some way to do it, it's not very straightforward. I tried to use the CollapsiblePanelExtender and had no joy. I didn't look at the source (don't have time, either), but I wonder if it's wiring things up with the UniqueID property of the controls.
Problems aside, I like how many problems are solved for you. Good stuff.