I'm wondering what the AI will be like in this game. We've already seen people doing lots of different activities - random people playing tennis, people jogging in the street etc. I liked GTA IV's AI, quite believable - NPCs did take part in different activities (you could sometimes see NPCs pick up prostitutes but I think that was also in earlier games). You could still exploit it for hilarious purposes though. For example, getting someone to accidentally punch a cop and then they start shooting at eachother.
The AI fucked up for me once - the police arrested this guy who started shooting at them, but one cop got left behind so he had no police car. What does he do? He starts to drive off in an abandoned taxi, and I actually got in the taxi and he just behaved like a normal taxi driver. I wish I'd filmed it, it was probably my biggest "what the fuck" moment in a game.