They use soy sauce in a lot of the marinades in Mexican cooking these days. :\ So you do need to be careful. Again, those dining cards are fantastic, I really recommend looking into them. They usually have them bilingual too, so if you're eating at a Thai restaurant it is in Thai/English.

Another thing to be aware of is a lot of times they fry wheat things and non-wheat things in the same oil.

The ways for cross contamination to happen in buffets is pretty endless. Someone could knock some wheat into a dish, use a spoon that was just in a wheat based dish, accidently dribble crumbs from bread. I remember one waitress on another gluten free web site saying how they're always getting crumbs from croutons mixed into the other salad ingredients, because they're rushing and food is flying everywhere.