Problogger is a site for blogging experts.
Here are the results of a recent poll of their users:

… two varieties of WordPress being used by 51% of ProBlogger readers.
This site runs on free WordPress.org software.
Rumours persist that WordPress.com will be acquired by someone, perhaps Yahoo!. Gladly the system is too good, too far evolved, to be ruined by anyone. Even Microsoft couldn’t destroy WordPress.