Dudes, seriously, this is so cool.
Stickers are micro-rewards. My mom used them to great effect in some part games she threw at my little cousin's b-day. The way she did it was to give each kid a "trophy card" (a cardboard placard in the shape and color of a trophy with their name on it) and after each game, award the winning team "3 stickers each" and the losing team 2, which each person got to pick out and put on their trophy card.
Then, at the end of the games, whoever had the most stickers got first pick from a bunch of assorted prizes on display. It was great.
Stickers are, like I said, micro-rewards. They don't replace trophies, but introduce another, more frequent, micro-sized reward system that can give players reasons to play again and again and again.
And the things you can do with them! Make a sticker book, or make sticker comics... GENIUS!
... my Mom's a genius too. Whatever little household innovation she does is SURE to be a consumer product in a year or two. There are spies in our house.
...wow... so awesome...