Just got this from CME, some might be interested.
Effective Sunday, January 11, 2009 for trade date of Monday, January 12, 2009
On Sunday, January 11, 2009, CME Group will modify the rules regarding the 5 percent overnight price limits for U.S. equity index futures traded on CME Globex during the ETH session. These modifications are designed to help preserve the market's ability to provide price discovery prior to the opening of the underlying cash market in all market conditions, without requiring a change in the overnight price limit.
Currently, if the 5 percent overnight limit is reached during the ETH session, and the market remains locked-limited until the opening of the Regular Trading Hours (RTH) session, the market's capability to provide price discovery before the opening of the underlying cash market is negated.
Starting Sunday, January 11, 2009, however, if the market is locked-limited as of 8:15 a.m. Chicago Time (15 minutes prior to the start of the RTH session) and still remains so at 8:25 a.m. (5 minutes prior to the start of the RTH session), the market will be halted and put into pre-open state. This will provide an Indicative Opening Price (IOP) in anticipation of a re-open on RTH, with the RTH limits in place - and effectively re-establish the market's price discovery capability.
This rule change applies to all legacy CME and CBOT equity index futures on U.S. stock indexes, including contracts based on:
S&P 500
S&P MidCap 400
S&P SmallCap 600
S&P 500/Citigroup Growth
S&P 500/Citigroup Value
SPCTRS
NASDAQ-100
NASDAQ Composite
NASDAQ Biotechnology
Dow Jones Industrial Average
Dow Jones U.S. Real Estate
Contracts on non-U.S. indexes are not affected by this change
Contracts that do not trade on CME Globex during the Extended Trading Hours sessions will not be affected