re: using two GCs for one check
We were just at Motown Cafe on May 4, and we used two $50 GCs. The waitress did look at them for a second (it seemed that she hadn't seen them before), but then said, "Okay, I'll be right back". Our bill came to $92, and she did not tell us we had to pay the tax separately, either. We did, of course leave a tip based on the full amount of the bill.
I got those GCs for $10 each, so that was one cheap meal!