Today SPY opened down about 0.8%. From then it has fallen even more, and in time of writing is down 1.5% since the open. A quite tough day for the longs.
Looking at what has happened on similar days since January 2010 (open more than 0.7% down and falling more than 1% from the open) before the last hour of trading, we get the following results: 5 fills, 5 winners and an average of 0.7% gain in the last hour of trading.