The value of homes are not upside down, they are coming down to there real value.
People got caught up in the hype and over paid for homes by 2, 3 , 4 .... times they were really worth.
I always have lived by a single rule when it came to house, they are for living in not flipping for a profit, that's where people got caught, they thought they were going to get rich on the house they bought and didn't think that is where they live.
Another problem was the home developers like KB Homes, these companies built new homes and sold them for outragous profits and they even had there own mortgage companies that made an additional profit. This was a big cause of homes over valuation.