You have to keep trying and pull out all the stops. Maybe you need to lower the price? There are buyers out there, but lots of choices and what buyers are telling us now is so many houses look the same, they're typically just buying the one they think they can work the best deal on.
Wait until June 09???? Holding on to a $500,000 house will cost you approximately $5000 in interest, taxes, insurance for a house you don't want. In June of 2009 there may not be financing avaialble, jumbo rates could be so high no one wants to purchase. Down payment amounts may have increased. Who knows what will happen to the market by then.
If you want to sell, NOW is the time to do it.....you just can't predict what the future will hold.