I don’t have an ad blocker on my work machine. The light web browsing I do on that machine mainly involves docs, internal resources, and sites like SO — which don’t have any ads or have very inobtrusive banners.
I really think we're approaching the point where this argument is the same as "I don't wear a seat belt when I drive to the corner store. It's right around the block and I never go above 10mph anyway."