Just a heads up, Google just announced the free $25 Play store credit with purchase of an N7 will be ending on 9/30, so if you are thinking about getting one, think faster...
Google Play credit on Nexus 7 - Google Play Help
As another note, you will have a year from that date to use your existing balance, all Play credit balances from this promotion expire on 9/30/2013
Google Play credit on Nexus 7 - Google Play Help
Eligibility
The $25 Google Play credit offer ends September 30, 2012.
As another note, you will have a year from that date to use your existing balance, all Play credit balances from this promotion expire on 9/30/2013