Seriously, not even hard. Learn it in a couple of days if you can program.
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www.compuware.com/Ajax-Edition Debug & Tune Front-End Performance, Drill into Client-Side Bottlenecks.
Sam Adams has written 2 entries about this goal
I’ve done a bit. Some quite weird stuff though. But I bet it was bug ridden. I guess it goes into production soon if they actually use it.
To me the main problem is the problem that the requests might come back in a different order. I guess then you should send information about what request the response is from in the XML. Some kind of nice wrapper would be good for this I guess. Maybe there is a good one, I don’t know. Maybe I’m wrong about it all, I’ve only done simple stuff really.
http://www.start.com/ That site is AJAX perfection though.