For my day job, I've recently had to read some stuff on power law distributions. Now I find it applies to blogging as well (Link via Hit & Run). Read the whole article, but the basic point is relatively intuitive:

"Though there are more new bloggers and more new readers every day, most of the new readers are adding to the traffic of the top few blogs, while most new blogs are getting below average traffic, a gap that will grow as the weblog world does. It's not impossible to launch a good new blog and become widely read, but it's harder than it was last year, and it will be harder still next year."