FilterKit is an open source project for adding Instagram style filters to images on iOS. This is just one of many open source projects created at last week's iOS Dev Camp in San Jose and it is really encouraging to see projects like this come out of community events.
I do love this feature of Clang which is now available to us in Xcode 4.4. Keith Harrison gives a nice overview of how to take advantage of automatic synthesis in Xcode 4.4 and also a couple of situations where it doesn't work towards the bottom of the article.
Mattt Thompson has started this beautifully named site which is intending to take a different overlooked Objective-C class each week and explore it a little. He only has four classes covered so far but I really like the style of this so I would put it on the list of ones to watch.
Remember the responder chain? This tip from Joachim Bengtsson is a good reminder that the responder chain exists on iOS.