Good to see that Apple have taken swift action on the IAP exploit of last week. If you use In-App Purchase then you want to have a good read through this document and the attached files.
Apple have revamped/replaced their Objective-C programming guide which so many of us surely used to get started with the language. Rewritten and updated to include everything from blocks and other reasonably recent advances right through to the new Objective-C literal syntax which only shipped two days ago with Xcode 4.4. The original "Objective-C Programming Language" document still seems to be available as of right now but I would not be surprised if this new version replaces it soon.
I hadn't come across this style of transition before but I quite like the idea. This implementation of the technique from Krzysztof Zabłocki is not only open source but does it using layer masks to avoid the lag of taking screenshots before peeling back the content.