A hotel I was staying at recently had some really neat walls in the lobby. I was in the midst of trying to capture all the curves and textures of the walls, when I was quickly interrupted by a security guard informing me that this was strictly verboten.
I tried to inquire a bit about the logic behind this, and I guess in our post-9/11 world, someone taking photos of the architectural elements of a building is likely a terrorist. Oops!
Managed to get off this one shot before I was sent packing.