i LOVE them for a few reasons.
game spice: they add FUN. no one remember the fight you did 10000 damage. every one remember the time you blinded the dragon who tried to fly and smashed the wall of the cave.
maneuvers is what make the combat different than world of warcraft games.
as for efficiant, well maneuvers are tools. like spells. and needed to be used when the time is right.
no one is trying to trip the 50 legged construct that has 50 CMD - like no one is casting a fire ball on the red dragon.
but when its right- it amazing.
a few non-conformist ways for using it:
the arcane :
our sorcerrer is using magic missile that trample all the time, its so great! especially when you can shoot at different opponents.
is shooting special arrows: tangelfoot, trip arrows and such to add fun.
me, the druid: i took improve unarmed strike and improve grapple with out dipping monk.... i grapple A LOT. when there is one opponent, when the foe is a caster and so on. with planar wild shape, CON of 16 and bear's i can last a while, holding the foe while the magus is killing it.
i am hardly optimazing and at level 9, saurian druid with Trex pet is mostly doing this:
round 1: casting lockjaw (second level spell) and fast wild shape to stegosaurous.
round 2: i hit once with power attack and vital stike doing 8d6 +magic fang+STR (22)+power att (+6) + bard buff = average of 46 pre magic items or reall buffs.
freely i trip (with bard buff, flank with pet, huge - good chance) and freely i grapple!
then, as move action i greater grapple again to pin the opponent.
if i am lucky, my foe is now a bit wounded but prone+pinned - wasting a round to get out while the group and trex is going for the kill.
not bad .