Kevin Lansing, a senior economist at the Federal Reserve Bank of San Francisco is worried. Well, not worried exactly but concerned, to use his term from an essay published yesterday, titled “Spendthrift Nation,” which of course is focused on Joe Sixpack’s unfailing fondness for spending, consuming and otherwise running up his debts. A smoking statistical gun, among many, is the latest trend for saving, which is to say the lack thereof. “In September 2005, the personal saving rate out of disposable income was negative for the fourth consecutive month,” Lansing wrote. “A negative saving rate means that U.S. consumers are spending more than 100% of their monthly after-tax income.” So what else is new? Everyone’s doing it, and it’s barely caused a ripple. Indeed, as Lansing reminds, declining personal saving rates have been the convention for the better part of the past 20 years. Why start worrying now? Lansing gives a few reasons in his essay, which we’ve added to the Research Room. If you’re inclined toward pessimism regarding Joe’s capacity to spend going forward, read on….