If you have an underwater house you are thinking about dumping you might want to get off your duff and list the thing. You see normally when you sell a house for less than you owe on it you get a nasty little surprise from Uncle Sam, a tax bill for the difference. During the bust legislation was passed to put this tax on hold to make it easier for people to short sell. However that legislation expires at the end of 2012. Both the Federal government and the California State gov passed these acts so currently there are no tax consequences from a short sale.
Of course the debt forgivness act could be extended. But what if it isn't? This would probably mean fewer short sales and a lot more foreclosures. There are no tax consequences from foreclosure because in Cali most of those loans are non-recourse (but I'm no tax expert so don't listen to me).
The unfortunate thing is that most people have no idea about this tax thing and may not feel the need to hurry up and get out while the gettin's good.