Although several years old, attorneys, financial planners and CPAs are still "getting used" to the relatively new portability rules. For decades, when it came to a person's estate tax exemption there was a "use it or lose it" rule which effectivley meant at the death of the first spouse, about half the assets would be transferred into a bypass trust so that the deceased spouse's exemption would not be wasted. However, with the new portability rules, one spouse's unused exemption is not lost, but passes to the surving spouse. As a result of portability, many bypass trusts have become unecessary and couples are preferring to have all assets pass to their spouses at their deaths--which not only increases flexibility, but which allows all assets to receive a step-up in basis at the death of both spouses.
However, portability may not be for everyone. In particular, where couples have had prior marriages, separate property, or children from a prior marriage, it may be that losing out on some of the basis step-up is worth it in order to help ensure that the assets are "locked-up" and secured for their benefit.