I've heard similar numbers quoted in the past, but it's good to have new research confirming things periodically. According to a study by Nielsen, "more than 35% of category sales storewide occurred on promotion; that equates to more than $129 billion in promoted dollar sales (not counting manufacturer coupons) through food, drug and mass merchandiser stores (excluding Walmart)."
The combination of a feature and display produced 176% lift, displays alone produced 87%, features alone 78%, TPR alone 44%.
The average promotional lift was 68% in the grocery channel, and 59% in drugstores.
By category, the highest percentages of promo sales were in soft drinks (63%), ice cream (53%), and crackers (52%)