Estate taxes for someone who lost a spouse in 2010?

For those whose spouse died in 2010, if the deceased's estate did not use all of the $5 million exemption, then the remainder can carry over to the surviving spouse. So if the deceased spouse's share of the estate was worth $2 million, then the unused estate tax exemption of $3 million can be used by the surviving spouse and added to the surviving spouse's $5 million exemption. Thus, if the surviving spouse dies in 2011 or 2012, the estate can pass $8 million estate tax free. However, there is no "stacking" of deceased spouses unused estate tax exemption if the surviving spouse remarries. Surviving spouse cannot pass the unused exemption to the estate of a new spouse.