Can't create an outlet by drag and drop ,Xcode 6
Not sure if you've managed to solve this issue already, but I just had a eureka moment myself. The problem with dragging-and-dropping was that I have re-assigned the left and right click on my trackpad, which ultimately led me to my solution (albeit in Xcode 7). 

To create an outlet, try to Control + Right-Click (or whatever your Mac's right click is set as - you should be able to find this in the System Preferences).