let start with some perfomance improvement tips which i used and it improved performance too.
but before starting it be sure that u have restored Vs2008 sp1.
It will give many new functionality.
today’s tips is Load Script befor Ui property in scriptManager tag of ajax.
Secondly if you require partial page rendering that use it EnablePartialRendering=”true”
just because of it your performance will improved.
you can use both the otption as shown below.