There are currently 750,000 fully activated Square Card readers. Half of the device users are individuals, Square says. Another way of looking at matters is that there now are 750,000 additional point of sale terminals in operation. As computers once were owned and used only by large companies, but become “personal,” so the POS now has become personal.

Square has 750,000 active accounts
Businesses that use the card reader range from farmers’ markets and taxi companies to personal trainers, contractors and plumbers.
Earlier this month Square announced that its readers were processing $4 million a day. Square is doubling the volume of payment performed over its readers every quarter.
Square has 750,000 active accounts (Wall Street Journal subscription required)