Obviously, this depends greatly on a variety of factors, as some sources may claim otherwise.
But according to VGChartz at least, the PlayStation 3 has overtaken the Xbox 360 in terms of global sales: 77,313,472 to 77,311,669.
It's safe to say the two consoles are essentially neck and neck right now, but there are two important things to remember:
First, the PS3 launched over a year after the 360 did, which means the PS3 has sold the same number of units in one year less time. Secondly, the catastrophic failure rate of the Xbox 360 undoubtedly resulted in plenty of multiple purchases from the same consumers; I've often wondered just how many of those 77 million sales were repeat purchases due to failed systems. Thirdly and lastly, PlayStation somehow always manages to sell consoles after a new generation is upon us. Look what the PS2 did in comparison to the Xbox after the PS3 and 360 were launched. Nobody cared about Xbox after the 360 arrived.
Therefore, is it safe to say that if the PS3 has indeed taken over the lead, that it will never again relinquish it? That may be the case. In fact, as you couldn't give away a Wii now if your life depended on it (hell, you can't even give away the Wii U), it seems the Wii will be stuck at 99 million units forever. Given the fact that the PS3 will likely enjoy two or three more years of really solid sales, it's perfectly feasible that it'll eventually overtake Nintendo's machine as well. Maybe it's inevitable.
And who, may I ask, predicted that at the start of this generation? Right around the time Sony had sold only a few million units and every last headline on the Internet was predicting doom and gloom for the PS3…?