According to Topps, the odds of receiving a a regular Golden Moments cards (the set consists of 100 players) is 1:15 codes. There's also a gold parallel (1:200 codes), as well as a 14k gold 1:1 version (1:20,000). Along with the Golden Moments cards, there's also 14k gold 1:1 versions of all 330 Topps Series 1 and 2 base cards, but the odds aren't much better (1: 6,666).
2012 Topps Golden Moments # GMDC-20
2012 Topps Golden Moments Gold Parallel # GMDC-20
2012 Topps Golden Moments 1:1 Gold # GMDC-20
Unlike in previous years promotions, you don't get an actual "vintage" Topps card with every code that you redeem. Since the odds of the Golden Moments cards aren't that great, you're more likely than not to get a virtual gold coin. If you collect all 30 coins in a single category (current MLB Stars, past MLB greats, MLB teams, with the rare 30th coin having odds of 1:6,666), you instantly win a signed Willie Mays card.
The cards themselves probably won't be produced and able to be shipped for a few months, but once they are, I'm sure they'll flood eBay fairly quickly.