The few problems I've had with Shadowplay is that it only does DirectX, so if a game uses OpenGL, too bad.
Also that you can't be on windowed mode to use it, only full screen.
You know the E.T. Atari game that was supposedly so bad it was buried somewhere in New Mexico?
Its real.
More Links:
http://kotaku.com/e-t-found-in-new-mexico-landfill-1568100161
http://www.kob.com/article/stories/S3413459.shtml#.U1wge_ldV8E