Nick Bilton, at The New York Times' Bits blog:

We skitter around the world with our smartphone cameras, taking pictures of leaves and sugar cubes and sunsets, then applying filters and making even the mundane look beautiful. Clearly, design is becoming increasingly more relevant to people. Google Plus doesn’t seem to understand that. Google’s iPhone app, for example, looks like a sketch that was never finished. And if you think the iPhone isn’t important for a good social network, just ask Instagram, an iPhone-only photo app that has more than 27 million users. That’s a quarter of Google Plus’s users, and Instagram didn’t need the Google homepage to get there.