I did my own tests with Google+. Some results:
- Google+ queues images for recognition. Results improved steadily over 72 hours.
- Google+ does not use OCR of text in the images. That surprised me. But perhaps it's a privacy issue.
- Google+ does use information gleaned from elsewhere on the web. Words that were associated with the same images on Flickr would turn up those very pictures on Google+.
- Oddly, Google+ does not use information associated with those images on Twitter.
- Google probably uses EXIF data married to a database of location names.
- The much-vaunted feature recognition is impressive, better than any other system, but for me did not achieve creepy levels of intuition.