Apple has made some very subtle updates to the visual design for iOS 5.
These are details so minor it’s amazing anyone even noticed them, and yet, they make a huge difference in the overall look and feel of the OS.
Makes me think of the Teehan+Lax iOS GUI PSD, which had to be overhauled substantially in order to bring it up-to-date with iOS 5. They documented a couple of the other changes in their blog post.