Valve announced that the Steam digital distribution platform reached 30 million accounts, an annual growth of 178% and 200% growth in sales. While the company cannot claim "accounts" being counted as "users", the fact that Steam has over 30 million active accounts speaks for itself.
When you compare the numbers, the closest digital distribution platform would be Microsoft’s Xbox Live and its spin off – Games For Windows Live. In February 2010, Microsoft marked 23 million active accounts, while Valve announced its 25th million active account in several weeks before, in January 2010.
Given that at the time, Steam only existed on the Microsoft Windows platform, the rate of growth is just astounding. In May 2010, Valve announced support for Mac OS X, which today makes for 4.46% of all Steam accounts [1.34 million]. Most popular operating system is 64-bit Windows 7, with 9.67 million accounts.
Valve also cites the Steam’s bandwidth expanded to 400 Gbps i.e. 50 GB/s – serving tens of thousands of concurrent game downloads at any time of the day. We also noted that Steam marks between 2.3 and 2.9 million users online at any time.