>>Hmm. Quick test:

        protected void Page_Load(object sender, EventArgs e)
>>        {
>>            theButton.Attributes.Add("onClick", "this.disabled=true; document.Form1.submit(); return false;");
>>          //theButton.Attributes.Add("onClick", "document.Form1.submit(); this.disabled=true; return false;");
>>
>>            if (IsPostBack)
>>            {
>>                int i = 0; 
>>                // If 'disabled' is first: Firefox - works. button disabled, postback
>>                //                         Chrome - button disabled, no postback
>>                // If 'submit' is first :  Firefox - postback, button not disabled
>>                //                         Chrome - postback, button not disabled
>>            }
>>        }

Didn't test IE...
>>>
>>>But, despite the fact that this no support was only referencing to other controls, I believe it might have applied also to buttons. The situation might be caused because of the usage of "true" instead of "disabled". That is why I need to complete the installation of IE, currently in progress, and take a look at this.
>>
>>Pls let us know what you find
>
>Before proceeding with more tests, can you adjust your code for "onclick" instead of "onClick"? I will only be able to test with IE 7 in about an hour. But, I think IE 7 might be case sensitive on that one. That would then explain the situation.

Case makes no difference. Couple of other things:
Safari behaviour is the same as for Chrome except:
With Chrome when 'submit' is first then subsequent clicks will queue the request so that postback is fired multiple times.

With IE the above code shows a null reference exception on the browser for 'document.Form1.submit();' , In this case if 'UseSubmitBehavior' is false then postback doesn't fire; if 'true' it does.

This code works as required with all of the above browsers (regardless of whether the submit or disable fires first):

 <script>
    function btnClick() {
        var b = document.getElementById("theButton");
        b.disabled = true;
        var f = document.getElementById("Form1");
        f.submit();
    }
</script>

and

theButton.Attributes.Add("onclick", "javascript:btnClick()");

I'd suggest using this instead.