I can't understand why more power pilots don't use it.
Me neither, makes putting it right where you want it a piece of cake.
Re the 172's, I haven't got the POH in front of me but one of our fleet is the 172K with 40 degrees of flap available. I'm pretty sure it says something like don't slip with full flap for the reason mentioned above, you get a bit of a nodding dog effect as it disrupts the flow over the elevators. Incidentally it's amazing the effect those last ten degrees have over the 30 degree flap 172's.