Don't use AJAX to call time consuming functions

Having an ajax exhaustive site can make performance go down if it has several heavy calls blocking the threads in the available thread pool - because the ajax calls calls a webservice wrapper and weservices are executed synchronously - compared to asp.net normal postbacks that can be asynchronously.
--> When having lots of load on such calls, perform partial or complete postback instead.

Found at: Dr. Dobb's AJAX ans Asynchronous Pages march 13, 2007