Disclaimer: I work on a competing job board site at Stack Overflow Careers 2.0
LinkedIn (as opposed to CareerBuilder apparently) isn't really cheating anyone. They're charging for a stupid feature to make a quick buck off of naive or desperate candidates. I can't figure out how a feature like putting a resume on the top of a pile solves any problem to do with matching candidates with employers. Much less why good employers would care about this arbitrary order. At least (apparently) they aren't biasing search results in their recruiter platform.
We've taken the route of only charging employers for access to advertise jobs and company pages on Stack Overflow, and search profiles of developers on Careers 2.0 (no crappy contingency recruiters allowed). Not only do we not want to charge candidates, I don't exactly know what we'd be charging them for that would help clear the market more efficiently.