Americans in their 30s and 40s — who saw their net worth almost halved during the Great Recession — are apparently botching even their most modest attempts at saving for retirement. According to researchers at Vanguard,almost 70 percent of last-minute IRA contributions remain parked in pathetically low-yield money market funds well after tax season. (How low? 0.02 percent low.) You have until April 15 to stash your $5,500 annual limit of IRA beans, so plant them somewhere they might grow into Benjamins. Read: Not a money market fund.