The CBO report on the estate tax has a lot of interesting historical information. For example, in the past the exemption for the estate tax was much lower:
The share of estates that were taxable rose substantially between 1950 and the mid-1970s, when that share reached almost 8 percent, but has declined sharply since then. Since 1977, generally about 1 percent to 2 percent of adults who died each year have left estates large enough to be taxable. In 2000, before EGTRRA was enacted, 51,200 estates were taxable, representing 2.2 percent of adult deaths in that year. EGTRRA reduced the percentage of estates that were taxable. For example, 17,400 taxable estate tax returns were filed in 2007; most were for deaths in 2006, when the effective exemption amount was $2 million, representing about 0.7 percent of adult deaths in that year.
Worth noting that as with much of the right-wing economic agenda, the growth performance of the American economy has gotten worse since we entered the era of estate tax cuts.