Clearly, a lot of Midwestern farmers own swaths of land and have seen their net worths jump over the past several years. Like Manhattan co-op owners who bought in the 1970s, these people are sitting on large paper gains.

But by no means do all farmers own their land. In Iowa, for example, some 45 percent of farmers rent all or part of their land. For these folks, rising land values have meant higher rent payments.

Worse, say you're a young person wanting to start a new farm -- say, a produce farm designed to sell fancy veggies to all those newly rich farm owners. You're now literally competing with hedge funds for land.

But I doubt the trend can last. At some point, corn-based ethanol just has to collapse under the weight of its vast ecological liabilities. When it does, corn prices will dive, taking land prices along for the ride.

And things are already looking a bit frothy, as the stock analysts say. One analyst says he expects farmland prices to rise at a 6 to 12 percent annual rate over the next three years, compared to gains in farm income of 4 to 5 percent.

In other words, land prices are rising faster than the income the land generates -- sure sign of a bubble.