Coupon etiquette?

What's the 'correct' social etiquette about using restaurant coupons purchased online (such as those from restaurant.com or groupon.com) when you go out in a group and split the check?

For coupons you get in the mail, or basically free stuff, I assume common etiquette is to offer the coupon to the group to use and split the remainder. Does it work the same way when you've bought, say, a $50 coupon for $25 (i.e. you use the coupon to cover $25 off your tab and offer the discount value to the group)? Do you use the entire $50 to cover just your tab? Or maybe simply not using the coupon when dining as a group is the right way to go?