The gadget is really great, but I missed some features. If you have always the same list in the same order in your sidebar, users very quickly ignore it. But if you shuffle the entries, the list looks fresh every page load. And I could not tell, which one of my most popular posts is the best, they are all good ;) and so random order suits them better.
I use a simple but effective Fisher-Yates/Knuth shuffle to shuffle the posts. You must have jQuery loaded in your page for the code to work. If the script did nothing to your popular posts list, try adding the following code, which loads jQuery, in your template before </head>: