The most complex aspect of estate planning is establishing a plan that will either minimize or eliminate any estate tax liability that would occur upon death. But it's worth the effort since the estate tax is one of the steepest taxes on the books.
In the case of a married couple, as long as the surviving spouse inherits the estate of the dead spouse and he/she is a U.S. citizen then there is never any estate tax upon the death of the first spouse regardless of how large the estate is thanks to the "unlimited marital exemption" (obviously, there is no such tax advantage for a single decedent). You could have a $10 billion estate, but there will be no tax due when one spouse dies.
The estate tax concerns arise when the second spouse dies and has not re-married, or if both spouses die simultaneously. If the size of the estate is over the $2 million mark, then the children will pay a whopping 45% federal estate tax on the overage!
This type of tax liability can be addressed in your wills or living trusts with complicated "AB Trust" or similar "credit shelter" planning (a good topic for a future post).
Please remember something that most of my clients forget or don't even realize: any proceeds on life insurance that you own are included in the calculation of your goss taxable estate!