Owner, world's coolest URL, Ma.tt
Seven years ago, at age 18, Mullenweg started a blog for fun. He has blogged ever since, and along the way, he created one of the world's largest blogging platforms. WordPress powers 14 million blogs, including many on this list.
On how to ruin your blog
"Don't Participate in Comments. Make it clear that your post itself is for anointed authors who don't mix with the hoi polloi in the comments ghetto...those people silly enough to contribute content to your site for free should feel ignored."