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http://www.xkcd.com/1133/
I think he's joking around a bit, "oxygen" is in the list, so is "thousand".

Here are the 1000 most used words, in order http://www.rupert.id.au/resources/1-1000.txt
I notice there are no bad words in the list though, how do they figure that? this is likely a problem.

Also this post is written using only those words. Would not have expected there to be enough words, but there you go.
I feel strange, not being able to draw from my list of favourite words. I think i tend to build what i say around such words, using them as key-words, land-marks.

It would be interesting to take whole paragraphs and draw lines up from each word in them, the lines' lengths based on how common the words are (longer = less common). Use it to compare people's writing methods.

I wonder how small you could limit the word-list, while still being able to talk properly at all.
200 could be interesting. http://www.rupert.id.au/resources/1000-words.php

I love xkcd.

On the topic of limiting oneself to the top thousand words, it's not too unlike witnessing my son's vocabulary expand. He recently turned four, and he's now up in the many-thousands of words he knows (he's fairly articulate for his age), but back when he was about two, it was interesting to see him trying to figure out how to tell us something with only the few words he knew at the time. Frustrating for him at times, certainly.

I think that line is the motto of the game Kerbal Space Program.