The one thing you generally expect of new, laboriously made products at restaurants is that they will be good. But even bad can be good if by "bad" you mean sour or bitter. The nation's avant-garde mixologists, mustachioed and otherwise, have taken up the creation of house-made bitters as part of their advanced drink programs, and their kitchen counterparts are following suit, with vinegars so complex and intriguing that they are sometimes served straight up between courses. Jonathon Sawyer serves half a dozen in tasting dishes at his Greenhouse Tavern in Cleveland. Happily, they are for dipping fries rather drinking, however.