Used to read him all the time, but much less so as I've become a better photographer. He's good for beginners. He speaks with an air of authority, which is what you want to hear when you don't know what you're doing. I think that's the audience that most benefits from his reviews--people who want to be told what to do.
As has been pointed out, you need to take what he says with a grain of salt. Mrdat pointed out above that Ken says he prefers his 18-55 to the 17-55. Clearly, that comment is not meant for me or for other people who know better. I also remember him telling people that you don't need a tripod with a digital camera. Again, not meant for me. Other times he says things that are perfect for people like me, and I've really appreciated aspects of some of his reviews--especially the comparison reviews.
The trick is to read his site and disregard all of the information that doesn't make sense to you. Even so, what he writes swings wildly from right-on-target to complete-and-total-crap.
My biggest problem with him these days is that I feel likely lately he's just trying to get as much stuff online as possible to reach as wide a base as possible to increase his ad revenue, writing reviews of cameras that haven't been released yet or of lenses he hasn't used, etc., and it has certainly compromise the quality of his content.
