The economy has added just 121,000 jobs a month in the 48 months since the 2007-2009 recession ended, barely enough to keep up with the natural growth of the labor force, according to MarketWatch. What is a "good" number for how many U.S. jobs are created each month? The answer is not as easy to figure out as it might seem, but one thing is clear: The economy is not adding jobs fast enough.