I'd probably sell if I was that far underwater. The market hasn't even reached a bottom yet, so you can always sell and rebuy once the market stablizes.

It's not like it's going to turn around over night from a sell off like this, the markets going to have to test a new bottom. And will probably trade in a range for a while before any form of recovery occurs. My guess is a slow but steady recovery, but I'm unsure of how low the bottom will be this time.