Browsed the thread.
My little one isn't eating peanut butter yet, but husband and I actually discussed (because it had come up on the television) the possibility that one of her classmates and possibly one of her dear friends in the future may have a severe nut allergy.
We discussed it while I was happily working on a spoon of peanut butter.
I've never been careful with my nut residues. If the she-tyrant brings home a friend that needs an epi-pen if nut dust blows on them, I'm going to be in for one heck of a learning experience.
It's not the same, but I imagine that when we're exposed to multiple children and the possibility exists that someone might have an allergy, I'll treat the situation the same way I behave when I'm feeding something I prepared to a group of people; I either know who abstains from what, or I announce the potentially taboo ingredients. For example, when I make meatballs and I say, to the group: "I made meatballs. They have pork in them." and this allows anyone in the group who keeps halal, kosher or eats vegetarian to skip the meatballs without a whole big to-do.
But I clearly need to educate myself on which foods are most commonly highly allergenic. My family has no food allergies so I have no idea what kinds of things people are allergic to. Except nuts, of course I'm aware of that.