Interesting New York Times article:  The "Death Tax" Lives on Despite Senate Republican Efforts to Kill It, by Floyd Norris:

In 2004, the latest year for which data are available, just 736 tax returns were filed for estates worth $20 million or more, and only 520 of them paid any estate tax at all. Those that did paid just 19% of their values, but that came to $5.6 billion for the federal government, or more than $10 million per wealthy taxed estate.

In recent years, the percentage that does pay taxes has been declining among the richest estates. That is perfectly legal, since any money that goes to either charities or surviving spouses escapes taxation. More money goes to surviving spouses than in earlier years, but less money is going to charity.

In 2004, 18% of the value of estates over $20 million went to charities, down from the peak of 28% in 1997. Elimination or a large reduction in estate taxes could prompt further reductions in generosity as the tax savings vanish or decline.

[Click on chart to enlarge.]