Samsung are showing a laptop that uses a 14" transparent OLED display:

The OLED is up to 40% transparent. I'm not sure if it's useful, but it sure is amazing. In any case, Samsung did not mention any plans to make this into a real product... Here's a short video:

Kyulux - Hyperfluoresence OLED emittersKyulux - Hyperfluoresence OLED emitters