Very, judgin by the amount that manufacturers pay in terms of reshearch and design costs. We are still a highly visual species, and attracting the wandering eye of the consumer is of considerable importance.
It's almost more important than the product itself I'd say. If the packaging catches your eye (for example looking at two different brands of the same product) then you are more likely to buy the one you like the look of if they are both priced roughly the same. It should be bright, informative and minimal I think to maximise sales though.