Obviously the chefs at Japanese and fusion restaurants have always known this, but I've just started cooking with the soy/butter combination more at home and it is so delicious. I started by adding some soy sauce to melted butter for popcorn, which is amazing. Of course it is good on fish, and last night I made some soba noodles and didn't have anything prepared to put on them. So I quickly sauteed some chopped garlic in butter, added lemon juice, soy sauce and sesame oil -- wonderful and so easy. Today I sprinkled seaweed/sesame sprinkle on the leftovers with shrimp for lunch.
I'm sure that's how a local restaurant makes their "tofu steak" taste so good -- they just drench the tofu in soy and butter. Not the healthiest, but it works like a charm when you need a quick hit of rich flavor.