I consistently score in the 45-47 range on verbal (GMATprep) and I rarely use the "extreme word" method.
If I have two questions that I'm having difficulty deciding between, I'll use the extreme word method to eliminate them, if I can.
That's not to say it's not useful, however, I usually eliminate such answers for other reasons (outside the scope, etc).
I think it is a good method. Anytime you see a word that is too broad or extreme, for example:
"the new policy will
always result in reduced profits"
"the proposal will protect
every endangered bird"
It's usually the wrong answer.
NN