For many recipes, firm tofu requires pressure to squeeze out the moisture. Pouring boiled salt water over the tofu gives you similar results in a fraction of the time.
We've covered how salt draws out moisture in salads and how salted water makes better french fries, and the same rules apply here. Soaking your tofu in salted water draws out the moisture and adds seasoning.
Vegetarian cooking blog Herbivoracious suggests this tip is best for crisping up pan fried tofu. Check the link for other quick tips on cooking tofu.
How to Make Tofu Really Freaking Delicious -- Tofu 101 [Herbivoracious via WonderHowTo]