I suggest that those who have upcoming assessment centres try to prepare for strength based questions. The questions aren't difficult or new. The only thing is the way they are asked can make it seem like they're trying to catch you out. Also, don't only bank on what you see on online forums....the strength based interview was with HR and one or two managers.
Group exercise, don't talk over others as usual and try to have good reasons for backing your team opinion up. Don't go in with a competitive mentality it won't help....it'll be really obvious to them. Don't forget it's not a competition....you're being judged based on what they perceive of you as a person.