If I remember my Cycling proficiency (Yes, I realise it's outdated, but it still sticks) it's taught here that 3ft out is about right for a cyclist (or 2ft at the very least) yet the amount of people that still cycle in the gutter or the door zone is unbelievable.
Exactly, it's surprising how many people don't realize that we cyclists need a "safety buffer" on both sides of us. Here where I live we have and advocacy group called the Florida Bicycle Association and they as with your Cycling proficiency class recommend leaving 3' between ourselves and the right side of the road so that if something comes at us from the right that we have room to maneuver around to avoid being hit by it.
Most day's I can count I don't know how many "gutter bunnies" when I'm out riding. The irony with them is that they then wonder why they end up getting flat after flat.
I will never ride in the door zone unless forced to do so by a motorist. When I am out riding if I encounter a bike lane that is in the door zone of on street parking, and there are any cars parked in the on street parking I avoid it like the plague. If there was a stretch of bike zone that the on street parking is free of cars I'll ride in it until just before the first parked car. If need be because of cars in the travel lane I'll slow my speed until I can leave the bike lane and pass all of the parked cars.
Back at the beginning of the month I had to laugh as some guy who had parked his pickup truck and was waiting to cross the street. Being as all of the parking spots were filled I was not riding in the bike lane, but rather out in the travel lane. I stopped to allow him to cross, and we ended up getting into a discussion about bike lanes. In his opinion because I was concerned for my safety I was an "effen a-hole " for not using the bike lane. He was of the opinion that because they (the city) spent the money on bike lanes that we should use them. Even apparently if they're unsafe for us to use.
I even tried to get him to open his car door so that he could see how far out into the bike lane it extended, but he didn't want to.