Marketing guru and author Seth Godin puts it this way:
"I don't blog to make money. I don't run ads on my site. I don't even blog to win awards. I blog because it pleases me to see my ideas spread. I like it when I see people talking about one of my ideas--without even mentioning where the idea came from. That means it's the idea that spread, not my brand. Which is the whole point."
Not to quibble with a provocative statement about the role ego plays in marketing... but I think there's a teeny little corollary here. When your ideas spread because people talk about them, it's usually because you're smart, your ideas are provocative and people respect what you have to say. Seth, that's part of your "brand," isn't it?? So willy nilly you are creating your brand when you blog.