On the first day of the company's annual Worldwide Partner Conference, Microsoft CEO Steve Ballmer revealed that, to date, Windows 7 has surpassed 400 million sold licenses. Despite this uber-success, Windows 7 is still behind Windows XP in terms of global use - 34.5% (for 7) versus 45% (XP).
Windows 8 was also mentioned at WPC but no extra details were actually given since Microsoft wants to focus on this OS at the BUILD conference in September. In the mean time Windows 7 can get back to selling very well so as to surpass 500 million in sales before its successor arrives.

Source :tcmagazine.com