Commonly, younger couples create a basic probate-avoidance living trust. When they're older, they revoke it and create an AB trust. And if one spouse unexpectedly dies sooner, the survivor will inherit everything free of estate tax, no matter what the amount. The surviving spouse will probably have years to use the money -- and to find other methods of reducing eventual estate tax.

Other couples who may not need an AB trust include:

• Couples where one spouse is considerably younger than the other. There's generally no need to burden the second spouse with a trust designed to save estate taxes when he or she is likely to live for many years.

• Many couples with children from prior marriages. There may be concern about conflicts between the surviving spouse and the deceased spouse's children, who must essentially share ownership of property for many years. (See Family Conflicts, below.)

Despite its possible drawbacks, an AB trust does work very well for many families. Many older couples conclude that the relatively minor accounting and recordkeeping hassles are outweighed by the benefits.