Eurobricks just put up a review of the minifigures.

Seems each box will give you 3 full sets and 12 spares, which ain't bad. Case breakdowns were:
5 Homer in his best suit and tie
5 Groundskeeper Willie
5 Bart as Bartman
4 Marge in a fancy dress
4 Lisa with Snowball II
4 Maggie with Santa’s Little Helper
4 Milhouse as Fallout Boy
4 Smithers
4 Dr Hibbert
3 Edna Krabappel
3 Comic Book Guy
3 Martin Prince
3 Professor Frink
3 Hans Moleman
3 Selma
3 Patty