To answer your question, Yes you can move out while your short sale is in process. It will make it easy for agents to show your property and get the process rolling. However if your home is in foreclosure the process of the short sale can delay the sale and you can stay until the process is complete. Like Scott said they may offer you cash for keys if the short sale does not go through and the property ends up foreclosing anyway. Talk to your agent or contact a short sale professional in your area to walk you through how it should work.
Realty World & Associates
Have you tried to give the keys (keys for cash) back to the bank holding the mortgage? I think they'd be interested in getting the deed back from you and possibly paying you some money for saving them a foreclosure proceeding. This is called 'deed in lieu'. Call them to discuss it.
Scott Miller, Realty Associates, Boca Raton, FL