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Lots of people have interesting things to say, but very few people have enough to say that I'll make their individual blog a regular destination. How many "sorry I haven't been updating my blog" blog posts have you seen?
Various kinds of aggregation are part of the solution to that problem, but some editorial filtering would really improve the aggregate. Also, I think a focus on slightly longer pieces would bring out a lot of cool stuff. On a blog, my attention starts to wander after a few paragraphs, but if I know beforehand that I'm going for something longer, and if I know someone is filtering out the dreck for me, I'm much more inclined to read an essay.
The editing doesn't have to be terribly labor intensive; some kind of community moderation would be great by itself.