That said, you should also keep looking, as there is always the possibility that the lender will counter at a higher number.. And, sometimes these homes get foreclosed on by another department while you are patiently waiting. I had lovely buyers who received a yes answer from the bank after waiting more than 90 days to hear...and two days later the bank foreclosed anyway. The short sale department and the foreclosure department are managed entirely separately, so you just don't know until you close escrow.
Hang in there on the offer that's accepted. Commiserate with your agent...he or she is probably equally frustrated and trying to stay positive. And keep watching the market.
There are so many moving parts to a short sale....hopefully your own agent has properly prepared you on what to expect. If he is also an experienced short sale agent, this would be one of the very first things he should have done prior to showing, and writing an offer on a short sale.