I wrote the Popularity Contest plugin for WordPress back in May of 2005. It had a good run, but that run is over. We are no longer developing or supporting Popularity Contest, and I recommend letting it rest peacefully.
Why? It does too much, and too little at the same time.
It does too much. Popularity Contest tracks each page load. In order to make this compatible with caching plugins, this functionality was abstracted to be done via a second AJAX call (or tracker image in feeds) that bypasses your site’s caching system.
In other words, with Popularity Contest enabled and a caching plugin installed, each visit to one of your pages still generates an additional dynamic page load request to your server. This is how it has to work, but it’s too much for most commodity hosting environments.
It does too little. While Popularity Contest is tracking each page load and updating aggregate numbers relating to your site’s activity, there is a significant diminishing of returns as you use the plugin over time.
There is no granular data tracked, meaning you cannot plot trends or view popularity in specific time slices. In fact, what I saw on this site was that the most popular posts became simply a list of what ranks highest for popular searches in Google.
With all of the free and low-cost analytics solutions out there, you’re better off using a service to get this sort of information rather than doing it yourself. I’d recommend Google Analytics, WP.com stats or more advanced solutions like KISSmetrics, Reinvigorate, etc.
While I don’t recommend reviving Popularity Contest for the reasons listed above, but if you’re interested in forking or looking at the code you are welcome to do so. I pulled a copy of the code from the WP.og SVN repository and put it up on GitHub. The wp30 branch probably works with the latest version of WordPress with few needed revisions.