Depends on your definition of ES. I see a wide variety of definitions some of them quite ridiculous.
My own definition gives a scale where -1 is "absolutely not an expert system", 0 is "heck I don't know" and 1 is "sure it's an ES".
I also believe that a system must actually do some good not just be a nice example to chatter about but never use in real life.
I also need to know how the system responds to small changes in inputs to judge how good it is.
Then each search engine is different. In the past some of them had block headed designs so were maybe negative scorers. I've not noticed a lot of continuous logics, which in my mind sorts the "nice try but no cigar" from the "good and has great potential".
So a pretty indifferent bunch among the search engines and they are getting worse. Partly through their own fault and partly not. There's a flood of rubbish content on the web (easy to publish) and they're losing out against that. Secondly some of them actively favour advertising in subtle ways, which is a direct move against being expert.
My best guess (without any serious work) there are probably search engines that are between say 0.01 and 0.15 of being a decent expert system. (Trend has been going backwards for many years.)
by Mike Gale: Make use of formatting available after sign-up but not during sign-up.