A unusual move in the skew index (which historically oscillates approximately between a value of 100 and 150) is especially interesting when it diverges strongly from the VIX , which measures at the money and close to the money front month SPX option premiums.
Basically what a 'low VIX/high skew' combination is saying is: 'the market overall is complacent, but big investors perceive far more tail risk than usually' (it is exactly the other way around when the VIX is high and SKEW is low). In other words, a surprising increase in realized may not be too far away. Below is a chart showing the current SKEW/VIX combination. http://www.zerohedge.com/news/2013-10-28/spx-options-skew-vs-vix