Went to a revolving sushi bar tonight. Everything was automated. They even had a touchpad where you can put in orders (like miso ramen soup), which get delivered by a belt. The only thing the servers did was sit us and bring us water. We asked them to replace a leaking soy sauce container and they never did.
We tipped 0$ -- there was essentially no service. I kinda felt bad, but talking it over with my wife, I couldn't really find a reason to tip.