Palfrey's life

I have a question for anyone more linguistically minded that's been kicking around my head for a while. This is regards Sapir-Whorf, and got triggered by the conversation with a linguist a couple of weeks ago (hey, she was cute...). Anyways, here's the question: I'm confused about what Sapir-Whorf is meant to be. The version I was arguing about on Boxing Day involved the idea that if you don't have a word for something, then you can't express the concept. Where as the Wikipedia entry and my own random memories seems to think that it's more about your language shaping how you categorise the world, and influencing your thought patterns in that way instead.

So, anyone here know any better? Anyone actually read any of the darn papers on this sort of thing?