Ronin, I'm with you. At buffet breakfast I would not tip. Tip? What for? I've done the work. All they do is clear lates and set tables which is part of the money that they make. Surely they do not live on tips alone?
I assure you when visiting Europe, it would not be expected. I have never seen anybody tip for a breakfast buffet.

Dinner is another issue and it is hard to quantify the what-ifs. Yes, I would tip and probably 15% at that. By the way, I always tip cash as that way it goes to the serivce provider and not divided up amongst the rest of the staff.