...seriously? I'm the only one under water so far, everyone else is positive percentages? :D
Ah, ARS, I like you so much, I'll de-lurk and play. We just sold my parent's house in SoCal. They purchased it 7/05 for 285,500. It closes today for a purchase price of 227,500. Note that this was an all-cash, no broker sale, so even though Zillow lists the value at 232K, we're still getting a fair market price net/net. The buyer was a neighbor and a probate attorney, so it was an easy transaction.
My parent's house was a new build and there are only three floorplans in their Del Webb development, so Zillow is probably pretty accurate. Before anyone starts boo-hooing, they sold the house we grew up in on 6/05 for 440k. It re-sold 9/14 for 220k. Ouch!
I think the fact that you are standing on your committment to the purchase price is admirable, ARS. IIRC, you're in the absolute epicenter of the real estate meltdown. Eventually, it will come back and you'll be able to enjoy the peaceful slumber of the righteous. Good on you.
As to the OP's question, we're in the middle of our first house flip, so I have no idea how to calculate this. We live in a paid-for >$1M clown house and own a rental property with about 50% equity (not the flip), I'd guess it's around 50% overall. Hey, CA real estate is expensive! Since the 50% of our NW that's not real estate is still a (to me) big-ass number, I'm not too worried about the actual percentage. I just know it's enough.