We bought one almost 2 years ago. You need time, patience, stubbornness, and a good inspector. And an agent.
Time and patience - you can't tell how long the bank will take. Ours closed relatively quickly because someone had put in an offer months before that expired, but the listing agent never told the bank so that the property wouldn't 'lose it's place in line' and that someone would get around to determining the bank's lowest acceptable price. (Many agents have figured that trick out by now.)
Stubbornness - Or a backbone. The day of our closing the bank decided that they needed more money and were trying to change around the agent's fees. Our agent called my DH, who got the joy of dealing with it. At that point the bank was just trying to scare a few more bucks out of the agents and us. We stood (mostly) firm.
A Real Estate Agent. They know the process. Ours wasn't familiar with it (not many short sales were clearing at that time) and was mentored by a more experienced agent to get it through. You may be able to make it work with the listing agent only, but I really prefer having a buyer's agent that's looking only out for ME. (And, odds are, if it's a shortsale the bank's going to try to get it's hands on the commission you think you're saving.) Our agent was responsible for all of the paperwork nonsense. You hear about them asking for resubmittals of paperwork multiple times? It was her problem.
A great inspector. Short sales are strictly 'as-is'. Bad stove? Your problem. Cracked foundation? Your problem, too. Make sure you know everything that's wrong or might go wrong and how much it's going to cost to fix. We got the appliance insurance (or whatever it's called) and ended up using it...only cost me $60 when my furnace thermocouple thing went out (just like the inspector warned it might) instead of much more.
Deb