Once had a B757 arrive that had been crew training all day around Bedford (Thurleigh) in low cloud icing conditions, and both horizontal and vertical stab leading edges had approximately 6" thick ice extending the complete span and wrapping itself around the complete L/E section. I questioned the crew as to whether they had experienced any handling problems to which they replied no, once they saw the ice for themselves they were as surprised as i was. Still it was a good indicator of what little difference ice on the tailplane L/E's makes.