Club Nintendo is a customer reward program. You purchase Nintendo products, register them on the Club Nintendo site and then you fill out a "brief" survey to earn coins that may be redeemed for prizes. If it was a grocery store chain, you'd have a little card with a barcode hanging off your key ring.
I was not quite as stoked this year as I did not find too many Nintendo games appealing enough to have amassed enough coins for Platinum status as I did last year. Barely cresting Gold status, I was pleasantly surprised to find the Gold option the better of the two freebies. Had the Platinum status awarded a Luigi hat similar to last year's Mario hat, I will readily admit I would have been disappointed.
With some of Nintendo's 2011 release schedule looking decently solid, I'm thinking Platinum status will be re-attained.