I have used this pattern in a few VF pages but since our upgrade to Winter 11 they no longer work. 

The correct param does gets does get passed in the POST, but never gets binded to property on the controller.

Ex:

    <apex:actionFunction action="{!refresh}" name="JSonSelect" rerender="selobj" >
        <apex:param name="firstParam" assignTo="{!selectedItem}" value="" />
    </apex:actionFunction>

Anyone else having problems with passing parameters in the actionFunction since the release of Winter 11?

-Tom