PR Blogger, Hans Kullin has done some research on which PR blogs are the most “influential” based on their Technorati references.
It seems from this research that Steve Rubel has the most influential PR blog.
In related news, Cameron Marlow’s Overstated blog has some really interesting analysis of the frequency that blogs and weblogs are covered in the print media. According to research from LexisNexis there have been 4051 articles since February 18, 1998.

Footnote:
Thanks to Robb Hecht for the head up on Hans’ PR blog findings.
Thanks to Trevor Cook for the link to Cameron’s research.