We recently had a developer on-board our project team who used every control he possibly could from the AJAX Control Toolkit. It was kinda cool but there were a couple of bugs that came along on a piggy-back ride with some of the controls.
This week, we just realised some of the pages had textboxes that didn't have focus by default. After a 3 hour effort, we realised it was due to the rounded corner extender that we applied on the panels. Getting rid of the rounded corner extender got the page working again. What we found odd is that when the page loads, the onfocus event of the textbox fires but when focus is lost on loading the rounded corner extender, the onblur event did not fire!
Anyway, I guess I'll stick to manually creating rounded corners for now.