It is notable that the VIX spiked up 16% on Monday and closed at the highest level since June.  In the past when it has closed at a high level on a strong move there has been a tendency for the SPX to bounce over the next few days. This can be seen in the study below from the 5/15/12 blog.  (Stats are updated.)

The numbers appear compelling. Below is a profit curve using a 2-day hold.

This study has been persistently bullish for a long time and certainly appears worth consideration.