Interestingly it seems to have been Microsoft internal slang much, much earlier. I used to work for a company that brought out an animation package for schools that we somehow got tied in to the Windows 95 launch. The boss got to visit Microsoft Redmond in summer 1995, and, while he was there, got his copy of one of the classic Windows programming books signed by its author. Petzold, possibly. In it, this luminary wrote "Nice app, guys". It was the first time any of us had seen that contraction used, other than in Win32 function names.

Peter