Where did all the money go?

I've got a simple question about the Credit Crunch? Where did all the money go?

I've always thought of money as something that is "conserved" in the physics sense, like energy. Money in = money out + money stored. So when someone "loses" money it implies that someone else got it. If I run a company that loses money, what it means is that I'm getting less money in than I'm spending on staff and supplies. But the money hasn't disappeared, its just moved from my pockets to my suppliers (and their suppliers, and so on).

But the financial institutions seem to have had billions of dollars disappear into thin air. They got poorer, sometimes so poor that they went bust, but nobody seems to have become correspondingly richer.

I guess this has something to do with fractional reserve banking, which I know doesn't conserve money. Suppose I start with £1000 and put it in a bank. The bank shows a balance of £1000, but it doesn't just hang on to my money, it loans £500 of it to Joe Bloggs, who spends it on a new TV, and the person who sold the TV also puts the money in the bank. So now the bank has $1,500 on deposit even though our imaginary economy just started with £1,000. So what happens if Joe can't pay the money back?

Can someone enlighten me?