I talked to a photographer from Kansas City last weekend while at a seminar who did a Groupon deal.
A $99 portrait with an 8x10 (unframed) print for $49. Studio only by appointment. Client comes in, he spends 10 minutes getting them posed, takes 5 pictures. Shows them the unedited pictures in Lightroom on his computer, they pick one, he gets them a print within 10 days they can pick up at his studio. Altogether he said he got the process down to 30 minutes per client and he says he's upsold 5x7's, wallets and larger prints to 75% of the people who come in with an average of $300 (must be a magic number). He also sells the 5 edited photos on disc at web resolution for $30.
He said he maxed out at the 2,000 limit he set and he set the expiration at 18 months. Restrictions include no evening or weekend appointments and appointments subject to availability. The deal expires this coming September and he said only about 35% to 40% have been redeemed. He also said that if anyone calls to make an appointment AFTER it expires, he'll allow them to use the Groupon as a "50% off coupon" and they'd only have to pay the remaining $50 balance.