[Time to get back something I'm more knowledgeable... what was I thinking getting into a discussion about MS??]
I have an article I have been wanting to write for one of the magazine's for almost 9 months... instead I have turned the ideas into a presentation that I'll give on June 20th (of 2007).
One of the precursors for this talk involves me doing a little bit of perf testing... well performance is a hard issue to analyze when talking web site, so instead I test the number of bytes transferred.
So my project was to take a simple form with 3 drop downs; each drop down provides data for the next one to be filled; when the last drop down is clicked data is written to a label on the form. Very, very, very simple form really, but big enough to begin to test.
My first step was to wrap an UpdatePanel around the whole form... and I accumulated numbers for each postback using fiddler (there were 3 postbacks).
Next I used the Ajax Control Toolkit's Cascading Drop Down Extender to remove the UpdatePanel from all but the label (this UpdatePanel is triggered by selecting an item in the last drop down). I measured the amount of data transferred in bytes (there were actually 4 calls back to the server with the cascading drop down).
Amazingly enough (although not surprisingly) the UpdatePanel's total number of bytes transferred was more than the solution using the Cascading Drop Down Extender. In fact the UpdatePanel actually transferred twice as many bytes (!!!)
The point is that just dropping an UpdatePanel into a form is not necessarily the best answer to ajaxify your web forms.
(BTW, I tested a couple other Third Party solutions and ended up with slightly larger numbers than the UpdatePanel)
Anyway, come to the Day of Ajax in Tampa of June 20th (of 2007)...