Having been here several more times, I would say that the most important thing to bring to Thai Square is a Thai friend. My first meal here was excellent, but having returned with non-Thai friends and ordering randomly, I must admit that there are a lot of subpar items on the menu.
Their curries tend to be sweetish, overly-unctuous, and bland. Essentially, they are no different than curries found in your local neighborhood Thai restaurant. Many of their noodle dishes seem quite Americanized to my palate as well. Also, after eating their crispy duck dish some more times, I can't get over the fact that all you taste is batter and honey and no duck. It was like eating dessert.
On the other hand, their papaya salad with pickled crab is one of the best dishes in Virginia, period. But, of course, it is off menu and I would never have ordered it if I wasn't with my Thai friend. I am beginning to think the popularity of Thai Square has caused it to dumb down its dishes for their increasingly non-Thai clientele and that they only really serve the authentic stuff for their Thai customers. It is a shame, but I guess that is what happens when you try to get Asian food on the East Coast (outside of New York, that is).