Taxpayers are permitted to use a value for estate tax return purposes that is six months after the date of death, instead of the date of death value (or at times, at dates after death but before six months). Code §2032. In 2008, the IRS published proposed regulations. Due to numerous issues raised with the proposed regulations, the IRS went back to the drawing board and has now issued new proposed regulations.
For those of you that would rather not read through them, a shortened summary can be downloaded here (click the link and then download from the box.net page that opens).