According to Sony, worldwide sales of the PlayStation Vita are higher than 2.2 million. That might sound like a lot of consoles, but in comparison to the competition, it's a disappointing number.
The 2.2 million number is for sales through June. As Joystiq points out. When Sony last let people know how many handhelds sold, it was May, and the company sold 1.8 million units worldwide, which means the console has moved around 200K units each month in May and June. By contrast, before the Nintendo 3DS received its price cut to $170, it had sold 1.41 million units more than the Vita's current lifetime sales. A month after the price drop, the 3DS was at 6.68 million units sold worldwide.
That having been said, the Vita showing at Gamescom 2012 was very impressive, I think you will agree, with a number of new titles and some impressive old favorites. I'm particularly interested in Assassin's Creed 3: Liberation. Check out the Assassin's Creed 3: Liberation preview; it sounds pretty incredible.