When we have the media howling that RE will never be a good investment again (and citing all sorts of reasons that sound good on the surface but fall apart under scrutiny) and the parasitic players (housewife realtors, "flippers", high-school dropout mortgage brokers, etc.) are driven from the market, leaving only the real professionals, then we'll know we're about a month or two past the bottom.
Oh, and I need to get my house in sale-able condition. Time to move up...