HI, I have good exp. in ASP.NET, C#, .NET Framework and all the RadControls including the RadAjax.
I am an independent programmer based out in Chennai, India. I have 12 years of exp in Microsoft technologies + a bit of Unix based technologies as well.
I have vast experience in improving performance/stability of applications and done system and design reviews for companies before. I can send my full resume, if you are interested.
Client side technologies like AJAX, ViewState and Server side technologies ASP.NET PostBack mechanism, ASP.NET Caching, using Session to cache large data objects etc. can improve the performance if properly used, otherwise could degrade.
AJAX will further enable to minimise code executed on the round trips between client/server, since the focus is on only certain controls rather than the whole page.
You can also try Runtime code profiling tools on the Server, to see which client requests take the longest time.
If you have more than 1000 concurrent users, you can resort to clustering and load balancing on the server side.
You can contact me at email@example.com