The thing that sucks, most people will read the $1million minimum and think that it is ok. Truth is, it really doesn't take much of a farm or business to be worth a million bucks. 150 acres, a couple of tractors, a combine, a barn, an elevator, and a couple of bob trucks and you're there. And you can't subtract the couple hundred thousand bucks of debt either.
Personally, it surprises me, as the the minimum was $600K at one point in time (when the last changes were made to the laws in 1981) and you'd think that they would reinstate that. It automatically increased to $2million in 2006, $3.5million in 2009, and went away in 2010. Of course, like all laws involving money, there is an expiration date, which was 2011, but Congress voted to extend it. They won't this time.
I have personally known three families over the years that had to sell farms because they could not afford the estate taxes, two more that had to sell significant parcels of land to get the money. There are also a few businesses that I suspect were closed for the same reason after the family patriarch died, but I didn't ask.
What no one realizes is that all cash has been taxed at least once, most real estate, equipment, merchandise has been taxed at least twice.
A pretty good history of estate taxes by the Heritage Foundation from 2004:
Estate Taxes: An Historical Perspective
An even more detailed history from the IRS (.pdf format):
http://www.irs.gov/pub/irs-soi/ninetyestate.pdf