Although I don't do it now, I have held an ADI badge (Approved Driving Instructor) since 1987, and still hold it so keep up on the subject casually just to keep my hand in. Well before I got back into cycling I used to tell my pupils that they should give a cyclist as much room as they would a stationary car - as a bare minimum. I used to tell them that a cyclist's head was probably going to be in the region of 6' from the ground and if he/she hit a pot hole the rider could be thrown sideways into the road with the head being 6'-ish into the road. So, if possible give them a couple of metres.
My employer for the last 8 years is part of the "public" sector and a couple of years ago decided to introduce bikes for us to get round a large site. They sent someone on a training course to train us and one of the things that came over quite strongly was called (I think) the Primary Position, several feet from the kerb. I understand the rationale behind this but personally it makes me feel very vulnerable. When I'm riding I tend to ride in what I consider to be an appropriate position for the situation, mostly just outside the grids on the left but rarely much wider unless the road conditions are really bad.
This is partly because I feel comfortable there and partly because I'm aware of not wanting to antagonise drivers. I don't think that makes me a wimp, but I'd rather rant on here about how close a driver got to me than have my obituary written.