Here's how it works: you are asked to select a definition for a word, and for every word you correctly identify 10 grains of rice are donated to people in need.
It's interesting to me because it couples helping others with helping yourself; even if you don't think about expanding your vocabulary as a "service" to yourself, it can still feel like a game. They demonstrate a degree of online marketing savvy by offering promotional items to embed in your content, e.g., the banner below.
It seems like there's an interesting insight here (help/develop/challenge yourself as a way to help the world) but they've focused exclusively on the individual nature of charity, and neglected the whole group aspect.
They've missed the boat on at least one important front: social networking. What if they had a FaceBook application that let other FaceBook users know you're participating and challenged them to do the same? Or sent me a grain of rice when they learned a new word? (think fishtank application). Also, why can't we play against each other? Play as teams? Rivalries could really accelerate the use of this utility, it seems to me.