As you would expect from NSHipster, this post sees Mattt Thompson take a look into the darker corners of the API diffs and highlights some less well known changes and enhancements coming down the line from Apple. I found the CMFloor and CMAltimeter classes mentioned here particularly interesting.
The extent of the new extension APIs in iOS 8 was one of the biggest surprises for me last week. I've been going on about needing better interop between apps for a long time but I was realistically only hoping for sharing extensions and had not dared to dream of all of the other goodies that we will be receiving. Andrew Cunningham takes a high level look at extensions and how they work. You might also want to check out Ole Begemann's take on how powerful extensions are going to be as well.
Chris Cieslak with a timely reminder that we shouldn't just be asking "How do I do this Objective-C thing in Swift?", but instead taking advantage of the new language to make things more explicit and understandable.
Evan Swick on some of the internals of the Swift language. It's not a huge surprise but there are a lot of similarities with Objective-C here. If this topic is of interest then you should also check out Jay Freeman's talk from AltConf.