Tempeh actually should be frozen, unless you plan to use it within a few days.
As Carolyn said, frozen tofu changes in texture (and color--it usually turns a bit yellowish). It's much more 'spongelike,' and holds marinates and sauces better (when you defrost it, squeeze out the extra water). It crumbles well, and is best for things like replacement for hamburger (like in chili, tacos, etc.). It doesn't work as well for stir-frying or blending, but it's good for baking. (And silken tofu--the asceptically-packaged type like Mori-Nu--doesn't freeze well. But it doesn't need freeziing to keep it for long periods, as the asceptic package does that. It's best for blending into puddings, dips, etc.)