When I bought my house, there was a hoarder across the street. His yard was filled with appliances and crap and the house was overflowing. He was the single point failure of a generally well kept block but I got my house pretty cheap. Eventually he disappeared, was arrested somewhere for something and the house was seized. The Emptying of the Rat House was a neighborhood event, we all sat out in our yards and watched them fill dumpster after dumpster. A single guy bought it, fixed it up and made us all very happy.
For you mildly disturbed hoarders, go to www.flylady.net.
I used to be somewhat obsessed with acquiring things, but now I am obsessed with getting rid of them. For the rest of us it is not so much mental illness as a wrong attitude about stuff and what its real value is. Now I lay up treasures in heaven.
My big problem was not that I had too much stuff, but that I didnt have enough space for all of it. Eventually the light popped on over my head and I realized I had plenty of space and too much junk. 6 lawn and leaf bags later I was feeling better. (And that was all out of various closets in the house). Still have all the stuff in the storage room to go through.