SUBSTITUTES AND COMPLEMENTS. I was going to just mock Lee Siegel's decision to revisit the blogofascism controversy, but he says something in there that I think is worthy of a serious response since I hear the sentiment from a lot of people. "Linking," writes Siegel, "is no substitute for thinking." This is true, but misguided. Compare it to "deciding which articles to print is no substitute for writing magazine articles." Obviously, the former is no substitute for the latter not because the former activity is useless, but because it complements the other. You couldn't have a magazine where nobody wrote articles, and the other things people do at magazines don't substitute for article-writing, but that doesn't make those other things useless.
If a blogger has a certain audience, and reads a post or an article somewhere that he thinks is insightful on some subject, and then links to it -- directed his or her audience to read the linked material -- that can be a very useful service as long as the linker's audience isn't a proper subset of the linkee's audience. Certain high-traffic blogs -- Atrios and Instapundit come to mind -- exist primarily as aggregators of other web content for their audience. Other blogs tend to do at least some of that kind of thing. Since the main characteristic of the blogosphere is that an absurdly large quantity of posts get written every day, that aggregation function is extremely useful. If The New York Times came to your house as a giant stack of totally random articles on various subjects, it would be totally useless. The people who organize the paper don't substitute for the people who write it, but they're crucial to the paper working as an information-delivery system.