I once built an app on their API for a hackday, and I had to film the demo because I could never get the devices to connect via a bump. It would happen like once every 5 tries.

Just installed it again to see the mobile to pc bump, and although the web app picked the device, my phone never got a confirmation. Considering I still have to download the pictures from their servers, Google+ instant upload does a pretty nice job in this department. Until NFC.