Square is probably the most formidable opponent to Google's push for the use of Google Wallet in retail stores. Not unlike Google Wallet, Square requires both the user and the retailer to have a special equipment -- an app for the former, and hardware for the latter -- to make everything work. And while Google has been struggling to get its infrastructure in place, even with MasterCard's help, Square seems to be taking off as the niche payment system right now. Square has just announced that it is processing over $10 billion in payments annually, and has increased its rate of transactions by $2 billion just this month.
TechCrunch notes that the $10 billion number doesn't even include payments processed via Starbucks, which just penned a deal with Square to set up its processing system in 7,000 stores. Maybe some of this pressure can get Google thinking about its Wallet strategy going into the future.