Yes. Usually a lifeboat. It can be totally obsturcted or partially obstructed depending on the lifeboat position.
SS Norway (12 times) '85 - '97; Radiance OS 06/01; Island Princess 11/04, Grand Princess 11/04/05, Golden Princess 7/21/06, Golden Princess 2/24/07, Explorer of the Seas 12/23/07, Island Princess 11/15/08
A friend had one of those cabins on a recent cruise that we were on and yes your view is obstructed. There was a bit of light coming into the room when the sun was on that side, but otherwise there's very little light. She didn't want to pay a lot of money for the cruise and that's why she chose a GG cabin which is much cheaper than the others.
It's almost like an inside cabin, but with a window and some light.