I follow a bunch of author blogs, but the most interesting and the most useful for other authors is undoubtedly Arthur Slade's. When he talks about selling books on Kindle, for example, he gives you actual sales figures, charts and graphs and a concise analysis.... I find I get more insight into the real life experiences of a (highly successful) professional author from this blog than almost any other. Unlike other authors who make all sorts of pronouncements on how to write or on the writing industry, Arthur just says, 'I've tried this and this is how it turned out for me' with the implication that your mileage might vary. And he has a lot of interesting ideas -- I like the discussion of losing weight while writing for example.
One basic principle that Arthur demonstrates by example is that if you want people to come to your blog on a regular basis, it has to be about more than just your latest book release. Slade's blog is fascinating: personal and yet helpful, accessible yet no talking down to readers. A lot of author blogs I look up are just announcements of book releases and accolades received. I seldom return to such blogs because they are ultimately boring even for the most fanatic fan. Slade includes lots about his latest book's progress so fans can answer the question "When is the fourth Hunchback book coming out?" but there is enough other stuff to keep the rest of us coming back again and again just because Slade is one of our more interesting virtual neighbours. I don't mind reading his commercials: I hadn't known the third Hunchback book was available until I returned to his blog to see how his experiment in digital book publishing was going, and then went out immediately and bought the book for my daughter. But I was there for the content. I humbly suggest that if you want readers for your blog, then you'd better have some actual content to hold their attention between commercials. The better the content, the more likely people are to refer friends to particular entries: I discovered Slade's blog because someone referred me to the entry on typing on a treadmill, and because I found that such an exciting idea, I stuck around on a regular basis for the rest of his blog -- including the commercials.