I know a guy that has one on his 96 Accord. I can't feel it kick in either. But when it does, he gets anywhere from a 3-7HP boost (depending on rpm's).
"Fastest (non-N/A) Zetec";
15.148 @ 90.21 mph (best time)
15.334 @ 91.61 mph (best speed)
Best 60' time = 2.297