We had an issue with Groupon/Living Social certificates being presented 3 & 4 years after the expiration date and i was obligated to honor the purchase value. That always irked me because the consumer doesn't have to uphold their end of the deal by using the certificate by date certain. Particularly when the justification I used to participate was predicated on 30% not being redeemed.
This bothers me to hear this from restaurant/business owners/managers. To me, the whole point of Groupon (at least, back when it first started) was to introduce you to new restaurants or businesses that you have never visited before. They, along with Living Social, introduced me countless new places - mostly restaurants. That is how I first discovered Burning Bush Grille, in fact.
I feel that if a business decides go the Groupon route, they take any loss out of their advertising budget. That's what it is - advertising, and trying to entice new customers or to remind those who haven't been in the past few years. It shouldn't be, in my humble opinion, used to make money in hopes that customers will purchase a voucher and then fail to redeem it.
Sorry for the sidebar. To stay on topic, I'll add this - if a gift card specifically says it is only valid at locations A, B, and C, I wouldn't be upset if I couldn't use it at location D. But if it does not list any restrictions, I would 100% expect my card to be accepted.