Sony revealed some sales figures for PlayStation 4 late last night. A total of 4.2 million hardware units have been sold worldwide and a healthy 2.3 million units of software (retail + digital). Furthermore, PS Plus subscriptions have increased a whopping 90%, which perhaps shouldn't come as any surprise as it is required for online play with PS4. Apparently 1.7 million gaming sessions have been streamed across Twitch and Ustream.