We all know that UpdatePanel is extremely easy to use and extremely power, it's the "start" control of the AJAX ASP .net technology.

But... all this ease of use means paying a cost in performance, did you know that updates panel brings all the viewstate in each request?

In this article, Jeff comments some internals about update panel, and how to extend it (e.g. making that only one of the controls get update, or performing a lite flicker to notify that the panel has been updated), and how to use other liter features of AJAX (more to code, but more efficient).