I can give you the comforting advice as CalGal gave you or the harsh reality advice that IPOP gave.
Comforting advice:
You don't lose the equity until you sell it. Hang tight, it may be a while, but the market will eventually recover. Just count your blessings, as it could of been worse : you could of bought the house in 2006 at a higher price or not be able to make your payment comfortably as you are right now.
Harsh Reality:
I would have to agree with IPOP's statements. Your same house is going for $575k as we stand now, which is right about the median home price of Irvine. Experts are predicting the median home price for Irvine could very well drop as low as $420,000 by 2010/2011. With a big recession, we may get there faster. Therefore, my advice is to hang tight and remember that you don't lose your equity until you sell.
Panda "BEAR"