Demonstration of how jQuery UI Block can be used to block the cetain portion of Visualforce Page while a Ajax Call is in progress.
Very simple from <apex:commandButton/> or <apex:actionFunction/> simply relate a <apex:actionstatus/> component which has a "onstart" and "onstop" event. Call the "blockElement" js function from the "onstart" and call "unblockElement" function from "onstop" attribute.
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1.Install the Package from https://login.salesforce.com/packaging/installPackage.apexp?p0=04t90000000LxcY