Dell has generated over $3m in revenue from its twitter accounts

"We’ve surpassed $2 million in revenue in terms of Dell Outlet sales, but we’re also seeing that it’s driving interest in new product as well. We’re seeing people come from @DellOutlet on Twitter into the Dell.com/outlet site, and then ultimately decide to purchase a new system from elsewhere on Dell.com. If we factor those new system purchases that come from @DellOutlet, we’re actually eclipsed $3 million in overall sales."
Source: Dell statement on their Community page, 11th June 2009
Healthy skepticism from the Guardian here