My mother hoards, but she has not gotten quite as bad as the cases I've read about. Things are not yet piled to the ceiling. She does, however, keep old newspapers and magazines STUFFED under her couch, planning to read them someday. She washes out and keeps old ziplock bags and has about a million plastic grocery bags stuffed into every nook and cranny. She buys clothes for her grandchildren and forgets about them until 5-10 years later when she stumbles across them in her closet. My sister and I hauled off several truckloads of PURE JUNK while she was away on vacation. She was NOT HAPPY at all!
She could not even tell what was missing, only that her closets and rooms were organized, therefore she knew stuff was missing! She immediately refilled the space.
That is exactly how my MIL is. She has a stack of newspapers on her coffee table that are at least 2-3 years old. She works at a department store and buys clearance items with the intent of giving them to someone as gifts. The pile of bags is taller then she is (five foot two) and almost as tall as me (five foot eleven).