On a lot of sites lately, I\'ve seen buttons being replaced with loading/thinking images after they are pressed, to prevent double clicks and make sure the user knows something
Go the simplest way. Say your button is btnSubmit.
Now using jquery, on click of the button:
The submit button will be disabled, the animating image loading.gif will show up. And the page will postback. The benefit is that if validation fails you can again enable the submit button and hide the loading image. In such case, obviously you will show the error message.