I just recently downloaded the latest public release of Xcode (6.3) and I noticed the storyboard for my app is now low res on my Retina MacBook Pro. Images, text and standard UI
It appears to be related to a bug in the newest iOS SDK, and as a workaround, they've forced Interface Builder to render everything at 1x. Currently, there doesn't seem to be any solution to this annoying problem other than to wait.