Prizes, badges and XP are earned when collecting the cards; even discount coupons. Valve's wording on their sign-off ambiguously points to the Steam Summer Sale?
It's near that time again when Steam erupts in an orgy of mega sales that just won't leave you alone. Sure you'll likely never play that obscure RPG but it's 90% off!!
"We'll be continuing to iterate on existing features and add new ones after the release. There are a few things we have talked about previously that we really wanted to get to, that have now been pushed till post release - Trade Offers, and the Card Binder. They will still get done we just don't have an exact timeline on that," posted Valve.
"For now until release we're going to focus on fixing up all the existing bugs and issues."
"Making trading cards available to all Steam users is a step towards an event we think everyone can be excited about..."
Steam's Summer Sales have ordinarily started around June's end, and so it would be quite advantageous to launch the Steam Trading Cards just before it all kicked off. Those cunning fiends. You'd best hope your wallet is braced.
For more info on Steam Trading Cards visit the official FAQ.