I have all of mine up in my attic un-flattened, and even up there they do consume a LOT of space. I've kept all of mine because in the past it really sucked not having appropriate boxes when we moved. Not that I have all of the boxes (including the giant JVC projector box and the really big Anthem MRX-1120 box) take up about 1/3 of the "bulk" stuff in the attic. "Bulk" meaning things that are just never being used, but not to be thrown away.
The ends of the boxes I have use packaging material, so I can't flatten them, but I don't recall if there is packaging material in the mid section. If not, that could be flattened like Mojo suggested.
