hmm, i know very little about linguistics, so ignore me if i suck.
but with tests such as the one fernweh described, or the stuff rsl12 was talking about... isn't it just as possible that people form languages based on their thought patterns, rather than vice versa?
for example, perhaps certain societies don't have words for similar colors BECAUSE they don't differentiate between them, rather than the other way around. the same goes for jokes, and literature... the ideas that can be expressed in a given language could be a product of those ideas instead of something that transforms them?
or perhaps its a combination of both. could the languages and the ideas interact in complex ways?