“U.S. stocks strike solid gains on second-quarter GDP,” ran a gleeful headline yesterday on MarketWatch.

“Investors, showing no sign of concern about the outlook, took the GDP report at face value and pushed stocks up sharply on the news,” ran another breathless piece of editorial, following data that showed U.S. GDP up 3.3% in the second quarter.

But as Addison Wiggan and Ian Mathias pointed out yesterday in Agora Financial’s 5. Min Forecast, the government’s stimulus check program and a weaker dollar were partly responsible…

Government stimulus checks helped boost second-quarter GDP up 3.3%. That’s nearly double the Commerce Department’s initial projection. A weak dollar also helped U.S. exports rise. They’re up 13%… 4 points higher than the expected 9%.

And for every bit of good news, says the 5, there’s a litany of scary data close behind…

Bankruptcy filings, for example, were up 29% in June, year over year. Total filings for the 12-month period rang in just under 1 million.

And here’s a curious bit of data for both Buffett and Greenspan, champions of the “American productivity” school of euphorinomics: Between 2000-2007, U.S. worker productivity increased 18%, but salaries declined, on average, $2,000.

Despite producing an average of 2.5% more geegaws each year, the median inflation-adjusted family has fallen over the past seven years, from $58,000 to $56,000. “It’s a compelling example of a large disconnect,” says Jared Bernstein of the Economic Policy Institute. “Americans aren’t being rewarded for their productivity.”

And as Strategic Investment editor Dan Amoss said in an earlier post about bond king Bill Gross’s plea to Barack Obama to boost the budget deficit to $1 trillion, GDP figures are not necessarily a foolproof measure of the health of the economy…

I’ve always been skeptical of GDP as a measure of economic progress. It treats dollars spent and dollars invested equally (a dollar invested adds to capital formation, while a dollar spent subtracts from it). The GDP equation also treats government spending as a good thing. It is not. Aside from spending on the occasional “public good,” it just sucks capital out of the efficient, adaptive private sector and doles it out to politically powerful voting blocks.

For the sake of U.S. stocks, let’s just hope investors keep on taking those GDP figures at “face value.”