So, from what I've gathered, I think we've reached a few conclusions:
1. Think about why are you setting the trap and hostile accordingly.
If its PvM, leave some warnings about. It will let others know to steer clear or maybe attract someone more adventurous to your party.
When it's PvP with a designated target, defiantly hostile them. You probably don't have to spoil how your going to go about it though. But give them a heads up.
The bridge troll is an interesting situation. I'd say hostile anyone that approaches and make sure you get your monies worth.
Another situation i thought about was an escape route element. Need to leave the scene in a hurry? Have a route laden with traps to make sure no one follows. Have it clearly marked though. Any one in pursuit will have to slow down to spot the traps least they step on a landmine...save for elves perhaps. Hostile your pursuers.
One more idea I had was complete area denial. Don't want anyone bothering you? TRAPS! EVERYWHERE! Let people know about the mine field though. In fact, go overboard with the no trespassing signs. Hostile everyone. Your not going to see anyone anyway...hopefully...
2. No exploiting transitions. Plain and simple, its a cheat.
3. Clean up after your self. Don't leave dangerous items laying around. Especially in trafficked/low-level areas.
4. These are some ideas I've had for new traps.
Lock Trap: Can only be placed on door. Will lock door behind person when closed. Disarmed using lock-pick or disarm trap. Higher level trap requires high skill. It could be used to lure victim into and indoor ambush.
Land Mine: Deals fire damage and has chance for debuff if victim fails reflex/will/discipline check.
Tripwire: Informs placer of trap, it has been tripped. Could let you know if you being flanked.
Trip Trap: If victim fails reflex save, victim is knocked down.
Thanks for your input guys