According to Valve, Steam now has 65 million active accounts, growing 30 percent from a year ago. At its daily peak, about six million simultaneous users are on Steam, with Dota 2 being the game with the most players on at the same time.

Steam has had big changes recently, adding Greenlight, Big Picture Mode, Early Access, Family Sharing, Trading Cards and Linux support all within the last two years. It also recently announced the Steam Machine and Controller. 

Our Take:
Steam's popularity is no real surprise because Valve continues to innovate and sell games at ridiculously low prices (a Halloween sale is happening right now actually). I'm interested to see if the Steam Machines and Controller will continue this tradition of success.