The IRS released Notice 2011-66 on August 5, 2011 which requires form 8939 to be filed by November 15, 2011 in order for executors to opt-out of estate taxes on 2010 decedents. Exemptions for extending the deadline are extremely limited so this should be viewed as a hard-fast rule.
If no executor was named for decedent's estate, for example, if the entire estate was part of a living trust, then the person in actual/constructive possession may also use this form.
This is important to note as opting out of estate taxes is no longer automatic. If the election is made by filing 8939, the carry over provisions of Section 1022 are then applicable.
Keep an eye out for the form as the deadline is approaching and the new form is not yet available on the IRS website.