San Francisco bakery Mission Minis was hit with 72,000 cupcake orders after offering a coupon on Groupon, an increasingly popular online service that offers a daily deal at local businesses in more than 140 cities. Mission Minis' bakers couldn't keep up with the onslaught, and some customers became angry. But the deal did increase orders overall, said owner Brandon Arnovick, and taught employees how to work under pressure. "It was fun," says Arnovick. "Kind of." Groupon said it plans to begin offering online marketing seminars in the coming months to better prepare small-business owners.