@phreaks: Sure, Citigroup purchased Wachovia, but Lehman's wasn't bought out by anyone. When banks go out of business with a massive 600 billion dollars in debt to creditors, all of the banks just stop lending to each other because they can't trust each other. When this happens and some concaine addicted juvanile on the stock market decides that such-and-such a bank isn't worth so much anymore, all of the investors panic, since if Lehmans can go bust, anyone can go bust, and if the stocks of such-and-such a company are plummetting and it can't lend from any other banks to support itself, it will get either bought up at massive underpricing or it will go bust. This spiral effect can happilly lead to a domino effect on the financial markets; but can also hold over into manufacturing and other industries, and when that happens we get massive unemployment, and all of those houses that people can no longer afford to pay off because they're unemployed will be repossessed and sold at current valuation - a massive amount less than the value of the mortgage.
Currently we should be happy that the financial market meltdown is just messing up Wall Street, but don't be fooled into thinking that only bankers will be the ones left picking up the pieces. The mess will hit the economy real hard when manufacturing and other big businesses find themselves unable to get credit or investment, and will go abroad or lay off staff.
I'm not sure why people keep on about the whole "markets will rectify themselves so we don't need to do anything" nonsense - the global economy will be OK in the long run, but when we all wake up from this financial nightmare you might find that all the jobs are in China, with America unable to afford to keep up technologically.
If the government can put enough liquidity into the markets to kick start it again, there's a good chance that the market will heal itself and the government can take it's money out later, even at a profit. If the government does nothing, there's a good chance that the market will tank the American economy.
With your regards to the Great Depression: It's not like the great depression YET, but the current situation is very simmilar to the crisis that sparked it off. You don't have to experience the disaster if you can see it coming and take evasive action.