Nice one ... pretty cool, I really like where this is going! Just donated some piggies.

I know this is a work in progress, so here's my feedback (I know it's a lot, but this could really catch on):
How many questions do you have in rotation?

How does it distinguish between same users with same/multiple addresses?

I think you should let the visitor know whether the answer:

is correct --> win piggies (animate/show coins going into wallet, or sound coins dropping in bucket)
incorrect --> try again tomorrow

I was thinking 1 question is not enough, maybe have like 5-10 questions in a row, and they get 2 coins for each correct question ... instead of the 1 question and they're gone.

Also, at the end, some way to share their score with their friends to make it catch on ...
At least a note to 'share with your classmates/teacher or something'

You could even have categories at the beginning: history, science, math, grammar, etc ...
Each category has a bank of questions.  The more interactive the better.