If you are a journalist or a young researcher with an interest in political blogs, you'll definitely want to check out this book: Typing Politics: The Role of Blogs in American Politics. The book gives a rather comprehensive and systematic overview of research results and popular thought on blogs and their role in a democracy.
On the upside, the author looks at many angles to understand the impact of blogs, such as: who the bloggers are (the author offers a challenge to the Internet optimists by pointing out that bloggers aren't the average Joes who've been empowered by the Internet - although such assessment is debatable and, even if we accept that premise, its implications aren't as clear cut as the author argues), who the blog readers are (the author offers a neat typology of blog readers ranging from commenters, to daily readers, to regular readers, to occasional readers), what is the nature of the relationship between the bloggers and traditional journalists (this is perhaps the most tenable and well thought-out part of the book), what the blog content is like, and others. The author doesn't only synthesize existing literature on the blogs, but also introduces his own original and interesting data that is used to build the arguments. Finally, the literature surveyed and cited is impressive in its comprehensiveness. The analysis of the literature is cogent and insightful. This book is the most thorough treatment of political blogs, as a socio-political phenomenon, that I have seen in the existing literature!
On the downside, the author doesn't specify the reliability coefficients (besides percent agreement) in the content analysis - which somewhat irks me as a social scientist. Some arguments go father than is warranted by the presented evidence - especially in regards to the predictions about the future influence of blogs and prescription that blogs should become more like mainstream media to be successful. I wouldn't be so certain in making any predictions about the future of blogs (especially in such a forceful manner that is employed by the author) given unpredictability of the technological development and the audience's use of this technology. I also disagree about the blogs having to become more like MSM in order to be successful. The point of blogs is that they do not need to rely on the advertisers, and they do not need large mainstream audiences to be successful - that difference from MSM is at the core of what defines the essence of the blogs. The author also uses only the most popular political blogs in the analysis. This is a defensible practice, but it clearly undermines the generalizability of the claims in regards to all political blogs.
However, overall the volume is a solid intro into the political blogosphere for the researchers starting to examine blogs; it also might be thought-provoking for those researchers who've studied blogs for a while. Overall - I'd recommend buying and reading the volume. The volume is among very few out there that deal with new communication phenomena in such a systematic manner.