In fact, I would advise my clients to hold their entire 401k balance in money market (cash) during a blackout period, just in case . . .
Excellent advice...I can't recall of a major spike to the upside during a blackout period, although I'm sure that has happened in the past.
Almost all investors are more afraid of a major loss in value than they are of a major loss of opportunity. Advising people often requires telling them that they must choose between fear and greed - fear usually wins.
In the case of Enron greed won, with the predictable result.