A common problem in developing with asp.net is the user pressing more than once on a submit button.
There is only one problem: When the button is disabled, the page is not submitted and the button event does not fires on the server.
Fortunately the validation library sets the Page_IsValid to false if validation fails or to true otherwise.
This solution changes the button image, but doesn't solve the problem, since the user can still press the button.
A more elegant solution is to use two Divs, on with the wait image and other with the button. When the button is pressed it's Div is hidden and the one with the Wait image is shown.
This solution works with ASP.Net Ajax and with ASP.Net validators.
The final step is to create a Server Control... :)