Isn't much of online coupon clipping debate 'gamification' though? Much of it seems to be based around when you can use multiple coupons on the same product, get a coupon accepted for a different product to the one bought etc.
I know how much traction the UK Nectar scheme has online (virtually none, despite being the currency of the 2nd biggest supermarket chain) and that is down to its '0.5p per point' redemption rate.