That system sounds nice in theory, but it doesn't work. Even places where virtual currency doesn't buy anything tangible, such as MMORPGs, develop black markets rather quickly.
If the virtual currency is worth real money, then the company issuing the virtual currency can make money by letting people buy into the system. I'd expect 99Dresses to start allowing people to buy "buttons" with real money after that have built up enough inventory in the system.
Sure, black markets are to be expected with any marketplace. Regardless, implementing virtual currency like this is arguably a more effective means to accomplishing their goals (growth/engagement/satisfaction) than not having virtual currency. But I could be wrong.. I guess we'll see.
