Well... It depends. There are blogs that are like
www.bookslut.com/blog, or Howard Dean's blog (or other such political blogs) that were keeping people involved/informed. Personal blogs... That's tricky. One could argue that they are a creative outlet, and that is a use. But one could also take your stance and argue that, Techrad.
Personally, I think that blogs can be great. When I started keeping an online journal, it only led to trouble. But I was only 12 when I started--I'm 15 now. As a 12-13 year old, most of my entries were angsty, childish, et cetera. Now I practice my writing techniques and keep my friends informed on all sorts of things going on in my life and in other places. I like to write about many things ranging from politics and current events to my own soul-searching... But my blog can also be an outlet for my anger or frustration, which I am very grateful for. I just switch the entry mode to "Private", and write down everything that is getting to me.
(Sorry for the long post here...)
So, in conclusion, I guess the usefulness of a blog depends on the writer's personality, what the writer intends to accomplish, and what the audience expects of the writer.