Why like a brand? Coupons. Plenty of coupons. "Oh my God, yes," said Ms. Williams. "If [Cheerios] started offering coupons, heck yeah I'm going to keep them around."

She isn't alone: nearly two-thirds of consumers in our survey said they want brands to offer them discounts online. In fact, the first reason they gave for friending a brand was "I hoped to get discounts."