Over a quarter of a million businesses have claimed their business on Foursquare

"Last year, we introduced the foursquare Merchant Platform to give businesses an easy way to reward their customers and find new ones. We wanted to give merchants a way to learn more about their best customers and start offering Specials to help them get new people into their location.
Now, over a quarter of a million businesses have claimed their business on foursquare. We’ve had everything from mom-n-pop sub shops to thousand-location national chains, and everything in between. And we’ve gotten lots of feedback along the way – about making it easier to create Specials, about different ways people have been growing their business, and about tons of fun ways businesses use foursquare."

Source:  Blog post from Foursquare, 9th March 2011