Online game Bigpoint generated revenues of over €2m in 4 days on sales of just one virtual item

"German online games publisher and developer Bigpoint made over 2 million euros of revenue this month on a single in-game item purchase.
The company's free-to-play MMO space shooter DarkOrbit, which launched in December 2006, has seen 66 million registered users in total over its five year life.
Earlier this month, BigPoint sold a special in-game item called 'The 10th Drone', which cost 1,000 euros to purchase, for a total of four days.
Simon Davis, producer on DarkOrbit, has now told Gamesbrief founder and Gamasutra contributor Nicholas Lovell that over 2,000 of these items were sold, meaning that over 2 million euros was spent on this single item over the course of four days."
Source:  Gamasutra, 23rd November 2011