Facebook mentioned in Internet.org's white paper this September that its members are uploading 350 million photos a day, or nearly 2.5 billion photos every week. The company is clearly beating Google+ in terms of volume, but it also has more than twice as many active users, a seven-year head start and frequent cross-posts from Instagram. That Google has reached 60 percent of Facebook's image traffic without those luxuries shows that it's doing something right for shutterbugs, even before today's upgrades.
Some of that group is no doubt relying on Google+ solely as a hosting service -- out of those 540 million users, 300 million use the social stream. Even if only some people are posting directly to Google+, though, that still makes it a valuable place for sharing pictures. And many are genuinely interested in socializing; for proof, you just have to look at the relatively high number of pro photographers who've embraced the service. Well-known pros like Lotus Carroll and Trey Ratcliff spend a lot of their time on Google+, and some of them have millions of followers. It's reasonable to believe that large numbers of those fans are sticking around.
Mark Zuckerberg and crew don't necessarily have reason to be worried in light of Google's expansion and new photo technologies. Facebook has been improving its own imaging features as of late, and photography is just one piece of a bigger social networking puzzle that includes games and location-based services. However, the rapid growth of Google+ as a photo platform shows that it's filling a void left by its rival. Vic Gundotra said at Google's event that images are some of "most important things we have," and it's clear the company is banking on that to draw us in.