A decade ago, limoncello was virtually unknown in the U.S., outside of Italian-American families that made their own. Now the sweet, lemon liqueur from Southern Italy's Sorrento Peninsula is something of a fad -- one that had its pop-culture moment back in November when Danny DeVito stumbled onto a morning television talk show fresh from an all-night limoncello bender with George Clooney. In today's bleary celebrity culture, no sort of notoriety is allowed to escape commercial exploitation. Thus the announcement this month that Mr. DeVito is lending his name to a new brand of the lemon juice. Let's just hope...