Google says 5 million Cardboard VR headsets have shipped so far

Google released numbers showing the impressive growth of its Cardboard VR platform. “5 million Cardboard fans have joined the fold,” Google’s vice president of virtual reality, Clay Bavor, wrote in a blog post. This suggests a real user base emerging, less than two years after Google first launched Cardboard.
Meanwhile, Facebook’s considerably more expensive but more computationally powerful Oculus Rift only has users by virtue of its developer kits, the consumer version is still several weeks away from shipping. Meanwhile the HTC Vive is not yet available for preorder. The size of the user base for the Samsung Gear VR headset has yet to be released.
In addition to the number of headsets shipped, Google is also pointing out that there are now: 
More than 25 million installs of Cardboard apps through Google Play
More than 350,000 hours of YouTube video content that people have watched in Cardboard mode
More than 750,000 panoramic photos people have taken with the Cardboard Camera app
And Google has now figured out the top five Cardboard apps: Chair in a Room, Vrse, Lamper VR: Firefly Rescue, Caaaaardboard!, and Proton Pulse.
Google is also pointing out that more than 500,000 students have taken Expeditions virtual reality field trips.
The adoption of Cardboard, which needs an iOS or Android phone to work, has been quick, and that should catch the attention of other companies interested in developing virtual reality.