Speaking from personal experience, Square is as Square does, totally awesome, in "G's opinion" : Buy stock now, tomorrow may be to late.
Snippet from techcrunch:
For background, Square offers an iPhone, Android and iPad app which allows merchants to process and manage credit card transactions with a handy little credit card swiping device that plugs into the headset/microphone jack. The device and service is the brainchild of Twitter co-founder and recently appointed product lead Jack Dorsey and Jim McKelvey. And Square recently raised $27.5 million in new funding, and announced a strategic investment from credit card company Visa. In Q1, Square did $66 million in payment volume (the company expected $40 million) and is now in track to process $1 billion in payment volume within a year.