There is another interesting story on Blog trends:
http://www.cre8d-design.com/blog/2006/05/12/google-trends/

And try this one keeping in Mind that mambo is not a unique word:
http://www.google.com/trends?q=wordpress%2Cdrupal%2Cmambo%2Cjoomla%2Cgeeklog%2C&ctab=0&geo=all&date=all

Another good resource for Geeklog fans:

CMS Critic

There is a review there as well: http://www.cmscritic.com/archives/5-Geeklog-1.5-Content-Management-System-Review.html

Wow thats alot of sites using geeklog lol.

I think Wordpress has the most users, then Joomla. But it doesn't mean that Wordpress is the best CMS. Wordpress is the most simple CMS for non professional users. Joomla is easy too. Geeklog uses less because it needs more professonal users.