Are you a hoarder, or have experience working with hoarders?

I've been really intrigued by the recent TLC shows on this difficult affliction, because my younger sister is a compulsive hoarder. But her disorder seems a little different from what I see in some older people. I hear many of these people, when asked about specific items they're holding onto, say they're keeping it because "somebody could use it." What I can't figure out about that type of thinking is why haven't they given it to 'somebody' rather than keeping it buried in their house for years. Do they really intend to give it to someone, or do they have a no-waste mentality carried over from a previous period of scarcity in their lives?