Squalor Survivors is a website for people who are dealing with or have relatives who are dealing with hoarding to the point of dysfunction. I grew up with a mother with this problem and I have pack rat tendencies myself, which I regularly battle with so I don't end up with a house like my Mom's. Moving has actually helped since it periodically has forced me to really pare down. I just thought I would pass this on for anyone who has ever suffered in this kind of environment or knows anyone who has. It's one of those things that most people suffer in silence.
Wikipedia also has a good page on compulsive hoarding.