Historically low unemployment looks great, but April's jobs report carries a warning

Historically low unemployment looks great, but April's jobs report carries a warning  CNBC US adds 164000 jobs in mixed April report  BBC News US adds a modest 164000 jobs; unemployment down to 3.9 pct.  Boston Herald Analysis: Falling Unemployment Rate Highlights Tensions Facing Fed Officials  Wall Street Journal Unemployment Rate Hits 3.9%, a Rare Low, as Job Market Becomes More Competitive  New York TimesFull coverage