Just to clarify: you are only going to allow users to answer 10 questions per day, max?
That's correct, it's all controlled by the web services. Ten random questions are picked per day from my database of questions and presented to the user. This means it's a level playing field for all, i.e. the same 10 questions for all users, which makes the scores tables more relevant. It also increases the longevity of the quiz.