What are the pros and cons of author blogs?

I have to disagree with Steve here, actually. I suggest that the critical question isn't whether an author's weblog is aimed at promoting a single book or group of books, but whether the author is blogging about something they're already passionate about.

After all, passion is one of the secret ingredients of a successful weblog, as it is in almost any communications environment. Clarity of thought and accessible communications style is the other secret ingredient, in case you're wondering about my personal recipe.

But back to this question. Is it useful for authors to have weblogs? I believe that in almost all cases, if the author is writing about something that they're passionate and enthused about, something that they also have some knowledge or expertise, then, yes, a weblog can be a delightful solution.

At its simplest, a weblog is a content management system so at some level, the question can become "should authors have Web sites" and I hope everyone reading this recognizes that the answer is "you betcha!"

Why? Because almost all the authors I know -- and I know lots of published authors -- seek to establish a dialog and help communicate their ideas effectively as much as they want to sell some books and make the mortgage payment.

Take my favorite comparison in this vein: Two business authors, Jim Collins and Tom Peters. Both write excellent business books, but Jim hides behind a 'committee' that 'screens' contacts from his woefully out of date Web site JimCollins.com, while Tom Peters takes the opposite approach at TomPeters.com with an active and engaging Weblog, exclusive material available for download, and he even engages in direct dialog in the comments section of his Weblog with visitors who have something thoughtful to share.

Now, you tell me, which of these authors is promoting their ideas and engaging in a frank, open dialog with their readers and customers?

Since focus is another positive attribute for a Weblog, I'm afraid that I disagree with Steve on the comment about weblogs for large series. I'm thinking of the overwhelming and therefore useless dummies.com site. Nice book series, but when they simultaneously promote books on adoption, wine tasting, learning Chinese and PHP programming, it's hard to imagine a Weblog associated with this phenomenal breadth that'd be worth reading more than once.

But I'm just one author and blogger. What's your take on this question of whether blogs are valuable and useful for authors, either as a fellow author, or as a reader and consumer of books?