For those fortunate enough to have had money that unfortunately has been diminished by half, some of them can sue for money damages.

If your loss resulted from misinformation or out right fraud you can sue and recover a fraction of your losses. After lawyer fees one might not see an advantage in sueing. If you have a money market ffund with 10 different stocks there is even less likelyhood of recovering losses. IF it was just one stock like Lehman Bros you are out of luck since they are banckrupt but Merrill Lynch still exists as a subsidery of Bank of America so if you could probe intentional fraud you have a chance of winning a legal action.

Otherwise its just the risk of the game.

Having bought a house for cash I am looking at a devaluation of about $100,000 or more and have no legal recourse. I knew at the time I was buying in a bubble market but nor did I want to deprive my wife and kids of a home with a playful back yard during an age when they could most enjoy it.