iOS 6 Camera
We suspect the strength of the iOS app ecosystem is what propelled the iPhone to become the most popular camera on many photography social networks (including Flickr), but the default Camera app has always been a decent option, especially when it gained an optional grid.
In iOS 6, Apple's added a Panorama mode. You hold your device in portrait orientation and slowly sweep horizontally across the scene you wish to capture (if you're going too quickly for the device, you'll be told to slow down). This being an Apple feature, it doesn't provide you with any further options whatsoever.
Fortunately, the automated panorama stitching the Camera app does is generally excellent, to the point we happily ditched third-party apps of this type from our devices.
iOS 6 Photo Stream
Photo Stream was one of those typically Apple technologies: great when it worked, maddeningly frustrating when it didn't, and with almost no options to fine-tune it.
Previously, Photo Stream provided access to your most recent 1,000 photos and/or screen grabs, and that was it. These would be synchronised across devices and computers using the same Apple ID.
With iOS 6, it's now possible to remove images from Photo Stream, and you can now also share custom Photo Streams with other people, or with the public at large via a website on iCloud.com. Any custom Photo Stream can be left as it was when first set up or later updated whenever you like, and those you invite to it can leave comments.
Disappointingly, this is only a shared service in the sense of you sharing your images with others, not you all sharing together. If Apple adds some kind of group Photo Stream, this could be a killer feature; right now, it's certainly a nice-to-have for an ad-hoc share of a few holiday snaps, but hardly something that will worry Flickr or Facebook.