The Site Stats page on wordpress for your blog tells you things like how many views your blog has perday, which day was the most popular, and how many total views you have. It will also tell you how many posts you have made, how many comments are on it, how many people were referred to your site through links, and how many people came to your site because of a seearch engine.
I think that PR practitioners could benefit from monitoring their personal blog to see how many views were made on posts, and which one was the most popular. The post or posts that are most popular can let them know what their readers like the most and they can do more posts along the same lines.
Checking your client or companies blog site stats can tell you many of the same things as well as the amount of referrals can help you know where your business is coming from. If the company can know where the business comes from then they can target that audience. Also, the company should make sure to reply to/thank people for their comments on the blog to build better relations.