QUOTE (cgnao @ Jan 8 2008, 10:21 PM)

Notional value becomes real value when the loser in the derivative trade can't perform on the obligation.
The $500 trillion derivative mountain is shaking badly and will collapse. This is 100% correct, guaranteed.
Er, no, that's 100%
incorrect, guaranteed.
There's no sure-fire method of measuring systemic derivatives risk, but as a general rule when the loser in the derivative trade can't perform on the obligation then logically the counterparty is exposed to the in-the-money open market value of the contract.
At June 2007 the notional value of outstanding OTC derivatives as measured by the BIS was $516 trillion. That notional value is useful for measuring the size and growth of the OTC derivatives market, but it's a pretty meaningless figure in terms of actual risk exposure. It's called 'notional' because the amount doesn't really exist - it's just a value against which the obligations on the contract are computed against.
In June the BIS valued the gross credit risk (GCR) of all outstanding OTC contracts (i.e. the cost of replacing all open contracts at the prevailing market prices) at $11 trillion. That figure is down quite a bit from a few years ago when GCR was running at around 4.5% of notional - this was due to the low volatility and stability of interest rates and currency movements at the time (remember this was six months ago). It's likely that GCR has risen considerably since then, but I doubt it's more than $20 trillion.
Then you need to remember that this is
gross credit risk. Counterparty netting arrangements probably reduce that gross value to 20% or less, so we're perhaps talking about $4 trillion or so.
Now, I'm not downplaying the danger of derivatives here, and Warren Buffett is quite right when he calls them 'financial weapons of mass destruction'. It's quite possible that cascading defaults on even a relatively minor derivatives failure could send violent shockwaves through the financial system, but we need to get away from this $500 trillion figure as some sort of indication of what losses might be sustained in the worst case scenario.
Let's keep it real. Things are bad enough as they stand at present without the added hyperbole.
Edit: Just for clarification: a default on a CDS can expose the protection giver to the notional value of the underlying. This post was directed at the idea that the oft-quoted $500 trillion of notional OTC derivatives contracts could become real if all counterparties failed. The CDS market is only a small part of the overall derivatives market.