Way back in the day, a quarter section of land (160 acres) in the Midwest was a good farm. So the farmers grew old and then died, leaving their widows to rent out the land and move to town. Speculation is that cash rents for good farmland in 2012 might be in the range of $350 to $400 an acre (lost the link--might be farmgate). I may be old but I can still multiply $400 x 150 (cheating a bit) to get $60,000 annual cash income for my hypothetical widow.
Via John Phipps, Agweb reports the sale of a quarter section in IA for $14,350. I can't multiply that in my head but I guesstimate that's about $20 million. (The same land went in 1956 for about $538 an acre.)
Bottom line: there's some rich widow ladies out there. And the estate tax is going to become a hot issue.