Xcode 6: Build hangs and Interface Builder Cocoa Touch Tool starts allocating all RAM

In Xcode, right-click on the storyboard file and select Open As -> Source Code. In the source code editor, change the value of "useAutolayout" to "NO". Then, you should be able to open your storyboard as Interface Builder. I ran into this annoying issue. Now, all of my storyboard files created in Xcode 5 can be open in Xcode 6 now.