When referring to yourself in writing, what are the rules regarding third person or first person?

I visited Chris Brogan’s site to see how one of the most successful blogger, social media guru, expert marketer, etc. writes and organizes his website.  One thing I noticed is that most of his site is written in a third person, like the About page.  It’s HIS site, yet he is referring to himself in the third person.  Perhaps he had somebody write it for him, but I doubt it. My site is written in first person because not long ago I was in a conversation with my friend – whom I very much respect as a consultant – and he told me how he thinks that we should write about ourselves in the first person.  He says it’s more personal and I agree.

What do you think?

Is there a certain level of professionalism maintained by referring to yourself in the third person?  I’d really like to hear your comments.