1. You get a direct line into the thinking of important people in the field, think Jonathan Schwartz or Tim Bray (Sun), Miguel de Icaza or Nat Friedman (Novell), Bob Sutor or Alan Brown (IBM), Don Box or Robert Scoble (Microsoft), Adam Bosworth (Google), Dan Gillmor (San Jose Mercury News), Jon Udell (Infoworld), Steve Gillmor, Dave Winer, Doc Searls, and many others. It's unfiltered and in their own words. This means a lot of typos and misspellings (my blog being exhibit A of that), but also an up to the minute take, in their own words.The article also has an excellent tutorial on setting up a Bloglines feed like the one we use here.
2. Reading from a news aggregator is a *much* quicker way of reading news. For example, when I log in in the morning and hop over to Bloglines, in one interface I can see what around 70 people, along with news outlets like the NY Times, Washington Post, and Boston Globe, or groups like Java.net, the Mono Project, Google, or GNOME have to say. Sure beats visiting the hundred or so websites individually to see if they might have some updated content to read.
3. The group mind knows things that one mind can't. There's no better example of this than Slashdot, where a post will bring thousands of different opinions and facts together in one place. That sort of group aggregate information assembly is very difficult if not impossible for one person, but trivial for the blogging world.
4. You get a much better picture of the individuals involved; what they're working on, what their concerns are, sometimes even what their favorite restaurant is. It's a different way to build relationships. Not a replacement for personal interaction, of course, but one that has its place and has a lot more scale to it. If you're a PR/AR person trying to get my attention, for example, it might help to know something about me.
5. You heard it here first. Blogs very commonly have announcements and news long before the mainstream media has heard, digested, and written it up. It's a nice complimentary source for the mainstream media, and it's a highly effective tap into the pulse of important news and announcements. From How to Get Into Blogs, 101 at tecosystems.