The Sapir-Whorf hypothesis, in a nutshell, is "language influences thought." The classic debunking example is the urban legend, "Eskimos have over a hundred words for 'snow.'" This is often overextended to imply, "...and so Eskimos must conceive of snow on a whole 'nother level, dude!"

But our non-Eskimo language doesn't fundamentally limit our capacity to comprehend the nuances of snow. We just add modifiers (e.g., 'wet' and 'fluffy') to "snow", instead of using a different word. And, actually, it turns out the Eskimos use modifiers, too.

The Language Instinct is a great read. Pinker's got a real talent for popular science writing that's accessible but not dumbed down. Check out his first hit, How the Mind Works, if you're interested in general cognitive science.