Haven't read through all the posts, but after the first 5 pages I have to comment:
OK, I am currently a flight attendant for a major airline that serves peanuts on every flight. I also have been doing this for the past 15 years so I can say it with some knowledge.
If a passenger informs the airline of a peanut allergy we do one of two things.
1. If it is a mild or standard allergy we refrain from serving peanuts 3 rows forward and 3 rows aft of the person with the allergy. This is the most common occurrence. I will talk to the passenger once they board to make sure that is acceptable, and the allergy is mild. I will offer to wipe down their seat (it's leather) and tray table for them if needed.
2. If they have a SEVERE allergy the plane is cleared out of all peanut products, the entire plane is vacuumed before boarding, and the row of seats and tray tables the passenger with the allergy will be in is wiped down and disinfected. That is really all we can do.
During boarding, I will make a PA explaining the severe allergy and to refrain from consuming any products with peanuts. I will again repeat the announcement once we are in air and explaining our service.
Passengers understand, in all my years I have never heard one complaint about not being able to eat peanuts in either circumstance. Seriously, how hard is it to refrain from eating peanut products for a couple of hours? And we will always have alternative snacks to provide.
OK, hope that cleared up what the airlines do. Granted, I have only worked for one airline but my guess is that it is pretty standard protocol these days.