I'm surprised nobody has mentioned fire yet. Not the fact that it happens, but that Sims seem to think that the best way to respond is to go panic right next to the fire. At least in TS3, if I send them across the street to safety, they don't come running right back like in TS2.
And... I don't hate it, but it certainly can be interesting/frustrating what traits the game picks for NPCs... I hired a butler who I found out to be a Klepto. At least he only took the TV and not one of my large gems or compendium ingots.
Finally, might be a glitch, but anybody else notice that if a Sim has a Harvester in their inventory, they can't go into a pool? I learned that one the hard way when my inventor caught on fire - I sent him to extinguish himself, and when he got to the ladder he refused to get in, saying that the Harvester was in his way. (Thank the Great Llama for the unlucky trait, or I would've lost him.)