On a standard Salesforce edit page, when the save button is clicked, the button immediately grays out and prevents the user from clicking the button multiple times.  I'm trying to get the same effect on a VFP but I am having no luck.  Has anybody already done this?  I don't know if it's pertinent, but my save button is calling a method called Save in a custom controller.

<apex:pageBlockButtons > <apex:commandButton action="{!Save}" value="Save" id="saveBtn" /> </apex:pageBlockButtons>