GDC 2015 will mark the 13th anniversary of Valve's first public announcement of Steam, which has since become the leading platform for PC, Mac, and Linux games and software.
In the last year, Steam added new services and features - including In-Home Streaming, Broadcasting, Music, and user created stores - as it grew to over 125 million active accounts worldwide.
Steam now offers 4500 games, with 400 million pieces of user-generated content contributed by members of the Steam Community.
From the SteamVR thread
They went past 100 million in late September 2014, so it's only taken them 5-6 months to get another 25 million active users. 50 million up from January 2014.
Because people will try to downplay this, as always - active account = logged in within the last month