I was thinking about this thread today when I was touching up my chain before climbing a big Live Oak. My file seemed half-dull, but I figured it was 'good enough'. Well, my lil 3400 was cutting poorly enough for the guy to say "That's why I use the 020T, those Echos don't have any power".
Well, after finishing the tree I went and chucked that file and pulled out a new one. 2 light strokes on each tooth, and it cut like a banshee in the next tree.