I pre-ordered my N7 from Google. They sent me this email:
"To get you started with your Nexus 7, we've given you $25.00 credit to spend on Google Play. Pick your favorite entertainment from more than 600,000 apps and games, millions of eBooks and songs, thousands of movies, and a growing selection of TV shows and magazines.
Your Google Play balance is ready to use right away: to start, just go to the Google Play store and start shopping. During check out, choose "Google Play balance" as your payment method and enjoy your selection."
I haven't found anything I want to buy yet.