Installed this today, and just made my first purchase with my phone! Overall, pretty cool Would be easier if I had a Citi Mastercard. I used the prepaid card to go grocery shopping. I had $110 on there, and ended up spending $130. So, I had to throw in $20 more dollars to the card after ringing up the food. After I scanned it though, Google Wallet force closed on me, but the payment still went through. Overall, really cool.
The best part, is if you create a new Pre-Paid card through the app, Google gives you a $10 credit, right off the bat. Free $10, so can't go wrong there.