So far I've made just over $200 USD. Its pretty amazing people are buying tons of gear with real money. It just goes to show you that, yes, people in fact will spend real money to make their characters more powerful in this game. I sold gear in Diablo 2 via Ebay, and im happy that it is now sanctioned by Blizzard.
My Bro has made way more, ($350 ish) and we have a friend who has made well over $500. Better find good things and sell now while the market prices for great gear is high!