I think the idea is local people assemble a “flash mob” but call it a “cash mob” because people come in and buy something.  We’ve had these types of things organized by our local chamber where members come to a site and buy something and the word is usually spread with the help of Facebook.  

Here’s the blog post on it:  http://cashmobs.wordpress.com/  I think it’s a great idea and if you have a local business and are connected with other local businesses, you could start by organizing one for a business in your area.