That's curious considering the state of the U.S. economy, but even more eyebrow-raising because the dollar is valued so low. When the dollar is weak against other currencies, it means goods sold in the U.S. are cheap to foreign buyers.Americans are showing the world that we're still rich and still like to spend -- even outspend -- people from other countries."For every bidder that we lose because their portfolio has gone down, we typically gain another," Simon Shaw, head of Sotheby's Impressionist and modern art department told Reuters after its New York sale last week.Seventy percent of the buyers in the Sotheby's Impressionist and modern art auction were American buyers, and they weren't being cheap. The average sale was almost $6 million, according to Sotheby's. A couple of paintings sold for record prices: a Fernand Leger sold for more than $39 million, and an Edvard Munch sold for more than $30 million.The auction's total take was almost a quarter billon dollars.To be sure, not all buyers were U.S. based, and at last week's Christie's auction just one-third of the buyers were American. Still, the fact that art prices are going strong and the U.S. is in the game shows consumer spending among the wealthy may be down, as studies show, but not off the table.Art, as an investment, has held up well over time, beating or competing with stock market returns. Hard assets in a recession are go-to assets as they typically fight inflation. The art world may be gaining sales and ground because of that, as over the past two years both volume and prices have soared.Indeed, Beautiful Asset Advisors, which specializes in art as an investment, says the current environment is similar to the art buying frenzy between 1984 and 1990. Last year, for example, the Mei Moses all-art index, which tracks art sales, saw returns of more than 20%."This result dramatically out paced the 5.5% increase achieved by the S&P 500 total return index (where dividends are reinvested tax free) for the same time period," Beautiful Asset notes. (Meanwhile, gold exceeded both of these results with a return of more than 30%.)Many financial advisers are weary of art as an investment mostly because of the liquidity factor. You could own an extremely valuable piece of art, but with no buyer it's worthless as an investment. This is the fallibility of hard assets, as many people in the real estate market are discovering.Sophisticated art buyers caution others about purchasing a work to make money. They say a piece of art should be bought for aesthetic purposes first, value second.Two weeks ago the Santa Monica Museum held its "Incognito" event. There, the names of the artists were withheld and buyers had to choose their lots by appeal only.Famous artists mixed in with unknowns, and museum collectors vied with amateurs for pieces. Every year the same thing happens: someone pays several hundred dollars for a work worth thousands. At the same time, some collector ends up with a valueless turkey. The concept is great. It exposes the raw truth of art (that it's in the eye of the beholder) and scratches at the subjectivity of trading in art and collectibles.We Americans, perhaps, perceive that our buying power has shrunk. But we still outspend the rest of the world on a per capita basis. Our wealthy class is still large -- about 10 million Americans are millionaires, according to Affluent Market Research, garnered by the research firm TNS.The numbers mean U.S. buyers can well-afford to keep buying art. Prices are going up. But just like the rest of the financial world the big question is: For how long? Without the likely suspects -- European buyers who also hold the most amount of the world's wealth -- I'd be scared of the bottom falling out.After the art boom of the 1980s, remember, there was a big bust. Art lesson: Buy art to put on a wall, not in your portfolio.