Canon IS Lenses – worth it?

Bob Atkins discusses Canon IS Lenses in this article. He asks is it worth the extra cost?
He also asks if it beats an L series lens which is all academic to me as I’m not going to be spending that much money on a single lens any time soon!
Lovely example shots showing the strengths of both types of lens.
I’m waiting on my Sigma 18-200, el cheapo, but “it’ll do the job” I hope!