The Biggest Investment That Isn't

Apropos of today's earlier post, we were thinking about the conventional wisdom that one's home is usually one's largest investment. In light of the number of people walking away from their "largest investment," it's worth asking...if a person buys a home with zero down and an interest-only loan (as was the case for more than a few buyers during the boom time), is it really an investment at all? The only thing the buyer is risking is his credit score. There's no judgement or political statement implied by the previous sentence. Just an observation meant to spark debate.