I admit that this post has only the most peripheral of relationships to technical writing -- but I'm enjoying Free Rice so much, I had to share. It's a website that generates vocabulary questions. For each question that you answer correctly, the site sponsors donate 10 grains of rice through the United Nations. It adds up quickly -- my first night, I filled my bowl with 7320 grains of rice. (That's how addictive it is, at least if you love words.)
The questions vary in difficulty, and are assigned to vocabulary levels (up to level 50). If you miss a question, you move back a level; if you answer 3 questions correctly, you move up a level. The more people "play", the more the site can fine-tune the difficulty levels for words.