They can be fun AND educational. If you go play with words at Free Rice, you are donating food for every right answer to the UN World Food Program. It took me less than 10 minutes to donate 300 grains of rice. I think that's probably lunch for someone...hell, that's probably the entire day's food for someone!
Anyway. Go. Learn. Do something for someone else. I'm off to do just that right now.
(found by the hat)