I've been to all of the GG restaurants except Black and Blue (where a $50 GC might get you an appetizer)... I would spend it at Trattoria, hands down. Better bang for your buck, basically the same food as IK but (IMHO) a much more enjoyable environment.
Alternatively, go to Sanafir on a Tuesday when the menu is 50% off, which is pretty great value for an already reasonable price point. The food is good and the atmosphere is pretty cool.
I've given Glowbal Grill several chances and have never left satisfied with the food and/or service, Coast is delish but $$$, IK is basically a more expensive TIK, Society seems to be geared towards stereotypical Yaletowners...kinda depends on what demographic you are looking for...
Brunch at Glowbal is decent and patio is nice in the summer/spring. It is one of my mom's favorites for Mother's day brunch.
I used to work nearby and they had a $10 express lunch ( in and out in 45 min on weekdays) aimed at local workers which we would sometimes go to. They did better with Brunch.
with due respect - the responses are kind of funny -- i am not fan either - i know others who have expense accounts who won't go to this group of eating places either. I think that Italian kitchen is one of the group - every one raves about the big meatball (seriously) - can't say i'm convinced. But the cheese platter (fresh mozza) was interesting and then get something plain to follow --- we had a big table DEC 2011 wkd evening and ordered just about everything - and the plain items (closest to what it really was, ie chicken without a slathering of cheese and tomato sauce) were best. It was hit and miss tho presentation was nice. It was very noisy. I suppose that is considered stylish in a downtown scene. but not for us. The flower baskets outside are really pretty.
While the food at Sanafir isn't great it is mostly edible, and the "dining while lying on a bed" upstairs is wicked romantic if you have someone special to go with you. If you have options, pick someone who isn't a foodie and they'll probably like the food just fine, and be blown away by the setting and atmosphere. :)
I've had the brunch at Glowbal and whatever-the-one-on-4th-is-called a number of times, and you could do worse elsewhere. Ditto with lunch at Catch. Alternatively, you could always ask if you can spend the gift certificate on a bottle of wine and gently suggest that you would not be offended if they forgot to open it.
On a related note, it seems the Top Chef finale was filmed at Catch and Black & Blue.