On "Britain's Best House" Kevin McCloud actually commented that he'd had a lot of letters from viewers wondering why so many of the houses featured lacked curtains and hinting that the occupants must be exhibitionists. He then showed a house in full view of a coastal path which had no curtains (the owner said they were old fashioned and would spoil the "clean lines" of the architecture) - this house had a full length transparent window in the SHOWER facing the public footpath which seemed to prove the point.
Glass is great for "bringing the outside in", "flooding the interior with daylight" etc, etc. I like glass as much as any architect but I don't like staring into blackness from an artificially lit room at night. Whatever happened to privacy, security, coziness? - Not fashionable, perhaps, but still important to real people such as GNetters.
Curtains also help to absorb sound as do carpets, upholstery etc. Too many hard surfaces create an echoey, soulless space which can feel quite uncomfortable. But I have to admit I do like white walls, which reflect much more light than any other colour.