Well this is fun. Just had a little play with this and found it a great way of stretching your brain and testing your search skills. A Google a day gives you new challenges every day. It works like this: They ask a question, you find the answer, they tell you if you are right or wrong, you try again, or if you got it right you get a new question. Repeat at will.
Great stuff for students, great for the 5 mins at the end of the period when you need a filler, great as a challenge for all sorts of people, including me. And you can embed it on your blog. Love it.