Josh Abernathy with a post on Functional Reactive Programming and ReactiveCocoa. I am not sure I am convinced on this yet but I am a firm believer that it's always worth looking at alternative approaches to problems and so this is worth a read. Reactive Cocoa also hit v1.0 this week so reading this post might give you a good opportunity to check it out if you have not already.
Yari D'areglia with a well written article on subclassing UIControl to create your own iOS custom control. Some good stuff in here, I especially liked the technique of using a dynamic layer mask to create a cute little glow effect for the control.
So it looks like Pete Steinberger has been implementing UIAppearance proxy support in PSPDFKit this week and has written about a couple of gotchas if you are looking to support it in your own custom view classes.
Are you always forgetting how to find the mid point of a CGRect? Or how to convert between coordinate systems? Then Adam Knight has a handy diagram and some examples of CGGeometry for you.