It's not very useful. Knew some people in SF that budgeted 4-digit campaigns and had no discernible sales conversions. Maybe it takes time for the network effect to make it useful? If so, few have the money or risk tolerance to try it more than once. For store owners Yelp is a reliable bet.

The inherent problem is ad money spent by retail locations don't convert to more foot traffic like a Google ad can send more eyeballs. And incentivizing people already at your store with coupons or via an iPhone app is awkward.

FourSquare is the 21st equivalent of billboards, lots of voodoo math and promises involved. And some people get a cheap thrill out of tagging up boards but in the end it's still just a tagged up billboard out on a lonely highway.

But, hey, who would be dumb enough to turn down $20 million and a shot?