i've been fairly interested in this thread.
My O2 sensors on my 32 GTR went bust when my turbo blew and obsiously broke the sensor.
since then i got the turbos replaced to new ones, which are the 2860-5's and because the sensor was buggered the car would run like a real pig when they were plugged in. so i unplugged them. then a week later i spun a bearing!
i know bad luck hey!
since that i got a motor rebuild, forgies, new crank, race bearings, thicker head gasket,etc
but didnt replace the O2 sensors, they've only gotten installed today, but for about a month of not having them plugged in on the new motor the car has been runing fine.
getting around 15L/100km which isnt too bad, but that has been conservative driving.
going to pick it up today,
will post again to let you guys know if i notice any difference.