Here is a Los Angeles Times article by two political scientists about the impact of political blogs, like this one. They talk about who reads political blogs, whether they change any minds (they don't), their role in surfacing issues that the MSM eventually takes up (substantial), and the importance of the political blog readership in the political process (growing).
One thing the authors don't mention is that many political bloggers (including this one) have interests beyond politics about which they blog with some frequency. This non-political content possibly influences readership.
In addition to politics, Glenn Reynolds of Instapundit also blogs on music and photography. The guys at Powerline also blog about British soccer and local Minnesota issues. The folks who select articles for Lucianne.com run obituaries of semi-prominent Brits. James Taranto of the Wall Street Journal's Opinion Journal enjoys headlines which can be read to mean something else, and makes fun of writers who use metaphors. Matt Drudge includes movie and TV commentary in his news roundup, like a latter day Walter Winchell.
COTTonLINE wanders off domestic politics into climate change issues, and also often comments on the internal affairs of foreign nations, most recently Belgium, Bolivia, and Turkey. Plus we do travel blogging when overseas. And it is not unknown for us to blog on Harry Potter. I suspect how you react to the non-political content of a blog is a non-trivial factor in whether you read that blog.
