Tired of hearing about CDOs yet? So are we. But the monoline bond crisis is still there, still generating downgrades — and on Tuesday, Standard & Poor’s Ratings Services cut Ambac Financial Group Inc.’s [stock ABK][/stock] core credit rating further, citing concerns over continuing exposure to bad mortgages. The agency also cut the financial strength rating of the company’s bond insurance subsidiary, Ambac Assurance, to “A.”