Instagram just updated its app for iOS 7 with larger, higher resolution photos and videos. The UI has been simplified and more screen space is dedicated to images, particularly in grid view. Profile pictures are now circular, which is kind of a yawn but otherwise the refresh is, well, visually refreshing. 

Version 4.2 is available for download now and requires a minimum of iOS 6.

Images and video are larger and extend to the edges of the screen.
Taking a cue from Facebook's smartphone notifications, profile pics are now circular.