Google today released numbers showing the growth of its Cardboard virtual reality platform, and they’re impressive.

“5 million Cardboard fans have joined the fold,” Google’s vice president of virtual reality, Clay Bavor, wrote in a blog post.

That number, which reflects the number of Cardboard headsets that have been shipped to people, including those from third-party retailers and the ones Google and others gave away — suggest a real user base emerging, less than two years after Google first launched Cardboard at the 2014 Google I/O conference.

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

And Google is also pointing out that more than 500,000 students have taken Expeditions virtual reality field trips — although that statistic was released last week.

Nevertheless, 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 developing technologies, including, perhaps, Apple.