This plugin extends pixelpost by a weighted archive tag: This plugin takes the categories and displays their names while the font-size depends on the number of posts in that category, i.e., the more posts a category gets, the bigger the size and vice versa (similar to the weighted tag display).
You could see this addon in action on my website http://www.yann-michel.de/ until I dicontinued to use pixelpost and switched to wordpress instead. Feel free to drop me a note in case you face any errors or simply have a question, anyway.
BTW: This project is a simple upgrade to the old project (http://www.pixelpost.org/extend/addons/weighted-archive/) that reflects the alternative language. It appeared to me that the old project is no longer maintained. So I took the opportunity to extend the code.