|Damn, should have picked the adventure with physical deathtraps instead.|
Without much cajoling, I'm a convert to the horrific versatility and creepy visuals of Haunts from Pathfinder. One can find the OGL write-up for them at Paizo's PRD: Haunts.
As the intro states, Haunts are like a hybrid between traditional Traps and Undead creatures. Maybe with a bit of terrain/environmental Hazard in there as well. They can make use of spells not often associated with traps, allowing the DM to get creative.
Traps are of a binary nature, either they're armed and dangerous, or disarmed through roguish know-how or player mishap. Haunts require a resolution other than triggering them, thus they're a bit like a Puzzle, or a Mystery. therein lies the reason why I think they offer a stronger draw to pull players into the game. Even if it just gives them an additional reason to thoroughly wreck a place, like burning down the haunted house as the PRD example explains.
It's the primitive caveman part of my brain saying this, but killing something with fire that needed re-killing is a very satisfying feeling. Makes things right in the world.
As with any traps, puzzles, hazards or even undead, haunts are most effective when used in the proper context (that context could mean when players aren't expending it) and care should be taken not to overuse them of course.
Well, can there ever be too much undead? They naturally fill the spaces they haunt, leaking from the walls, overflowing from the toilets and showers, climbing out of screens...