I may be alone on this one, but I usually don't bring anything unless I am asked to. It is usually known before hand if it is a pot-luck or something where you have to bring something. If not, I suppose I usually figure that the host or hostess knows what he or she is doing. I am planning a house warming so everyone knows to bring gifts, but I really really, really don't want anyone to bring food. That would just ruin my whole theme.....
Plus, what if it is nasty or makes someone sick???? How embarrassing would that be!!!!