Here’s my take. A blog about a product cannot create fans. Fans of products are created from the experience the buyer has once they have used the product. The product creates fans not the blog. That doesn’t mean a product blog is useless, far from it. What a product blog can do is create excitement and intrigue and help persuade a person to purchase the product. But it can’t create a fan.
On the other hand, if the product is a human-being and his views and opinions (think Seth Godin), then yes a blog can create fans. The difference here is that blog readers are experiencing the product by reading it.
So before you make your pitch to your boss or client that a blog will create fans, think about what you’re implying. Be sure you’re not setting false expectations.