Promoting the library - Loyalty cards

An idea blogged about here got my attention.

Giving students loyalty cards for checking out and reading a book. The librarian says the student needs to be able to discuss the book briefly to qualify for a stamp on the card (similar to coffee shops). After ten stamps they get a reward.

I like the idea, although not sure if it would work in all schools - particularly larger schools, but its a nice fall back plan if borrower rates are low. It could also work during special one-off periods, or perhaps only themed books qualify.

However, does rewarding reading with external motivators remove the internal rewards we gain from reading? Can reading be its own reward for all readers?