Out of interest, I too am working on a general knowledge quiz.
What do your customers get if they pay for the quiz?
What incentive is there for them to answer the questions on your quiz?
I had 10 beta testers but they could only test so much, therefore the app is free at the moment to encourage a lot of users to play the quiz and make sure there are no issues with a large user base before I start charging. I don't intent having a lite version, it will hopefully be paid for (as long as the testing works out). In the 2 days since launch I've had over 500 people playing.
I have three ranked score tables in the app, daily, monthly and yearly, so the incentive for the user is progress in these tables. Users can also submit their own questions, with the obvious incentive that if their question is used, they will know the answer.
One issue I have is the global nature of it and time zones. The app provides 10 fresh questions at midnight GMT, so those elsewhere get them at different times. No way round that I reckon. My web server that dishes out the questions etc is in California so needs an offset to sync with the app.