Bill Hobbs has a post pointing out that a link in a high traffic blog brings a blog more traffic than a mention in any "old media" outlet. Not to be facetious, but is anyone really surprised by this? As I see it, there are two reasons:
1. Ease of use: I mean, really, if you're reading a blog, and you see a link to something you're remotely interested in, you click on it. Easiest thing in the world. Now, if you hear about it on television, or read it in a newspaper, first you have to get online, then type in the address. If you think to yourself "I'll do it the next time I'm online," are you going to even remember the intention, much less what the URL was?
2. Targeted advertising: People who read the big blogs are, after all, the people who, um, read blogs. If you see a link in a blog, then obviously you already know what a blog is, and you already read them, so you're the perfect audience for the link.