EDIT: terribly sorry for posting to the wrong section... my first post:(
Popularity Contest was one of the best plugins I used on my older WordPress 2.3 website: unfortunately, on 2.5.1 it does not work anymore.
Ken McGuire addresses the issue here:
I have taken a look myself and fixed the remaining problems that prevented the necessary tables from being created at initalization.
My patched version of the Popularity Contest plugin is unofficial, but works perfectly on WordPress 2.5.1. You may download it from:
I hope this helps someone.