So, I suppose you should just be able to see the fact that Ajax is working by the lack of page flashing. That may be true on a normal page on a slow connection, but if you are testing locally, it may not be so obvious. You can certainly crank up your debugging tools like firebug or Fiddler, or you can do the cheap trip about I’m about to explain.
Simply, add a sleep statement to your page_load event (Thread.Sleep(3000);) and run your page. If you are using IE7 like I am, on the post back (for a full page), you will see the windows icon spinning in the tab control. If you see that, you are getting a full page post back. If not, chances are you are not.
Hope this helps!