Japan has been using this technology for years now, so I would guess Google probably got the security part down. However, I think you will still need to carry your credit card… suppose your phone goes dead. But some of these things may not even be an issue, Google have some other serious problems with this.
PayPal Sues Google for Stealing Mobile Payment Secrets
PayPal has sued Google and two of its top execs, both former PayPal employees, for stealing trade secrets that helped the search company break into the multi-billion dollar mobile payments industry.
Hours after Stephanie Tilenius, Google's VP of Commerce, and Osama Bedier, VP of Payments, announced Google Wallet, a groundbreaking initiative to make mobile payments commercial, PayPal filed a 28-page lawsuit in California accusing Google and the two employees for misappropriating information and actively poaching other PayPal employees.
Tilenius joined Google in October 2009 as VP of Commerce after serving in various leadership roles at PayPal and eBay since 2001. Bedier jumped from PayPal's VP of Platform, Mobile, and New Ventures to become Google's VP of Payments in January 2010.
Rest of the story
http://www.pcmag.com/article2/0,2817,2386033,00.asp