A store front window in Miami Beach. Joe Raedle | Getty Images

The near-50-year low in the unemployment rate signifies that a lot of good things have happened for the economy, but also could point to some bad things that could happen. In fact, the last time the headline jobless level was lower, an economic downturn followed. December 1969 saw the rate fall to 3.5 percent, and it was at 6.1 percent a year later when the economy struggled through problems in 1970 that sound a lot like conditions now. The current unemployment rate is 3.7 percent. Back then, the economy was coming off what at that point had been its longest expansion ever, a nearly nine-year period of prosperity that came amid aggressive fiscal expansion to finance the Vietnam War.

Growth finally started to peak, though, as 1969 came around, and by early the following year, the expansion was over. That's the bad news. The good news is that what followed was a nine-month slump that is one of the mildest recessions in U.S. history. GDP was negative only twice during the year — a 0.6 percent decline in the first quarter, then a 4.2 percent drop in the fourth quarter. In between there were increases of 0.6 percent and 3.7 percent. And by the time November 1970 rolled around, the economy was back on its feet en route to a three-year expansion that saw GDP growth average 5.1 percent a year. In fact, some economists don't even count the 1970 downturn as a recession, instead considering it a pause in growth that quickly abated. Investing experts are conflicted over whether the current economy is just getting revved up, on its way to another 1970-style slowdown, or ready to tumble into a late-1970's-style inflationary spiral that will precede a much sharper downturn. GDP grew 2.2 percent in the first quarter this year and 4.2 percent in the second, and may have registered above-4 percent growth in the third quarter. "It doesn't give you a warm and fuzzy feeling when you see these types of unemployment rates," said Jim Paulsen, chief investment strategist at The Leuthold Group. "I don't really see very high odds of anything like the '70s. That said, I think we've got all the makings of a normal cyclical buildup in costs and inflation."