You should probably use the magic arguments array in your function to avoid the ugly array you are using as the second argument.

    _meq.push("track",["event_name",{property_name: "value"}])

becomes

    _meq.push("track","event_name",{property_name: "value"})

By changing the top of the mixpanel function to:

    mixpanel: function() { 
        var mixPanelArgs = Array.prototype.slice.call( arguments );
        var functionName = mixPanelArgs.shift();