After 30 days of teasing
                                
                                
                                    (Newser) -
                                    For the first time in 18 years, as  Marissa Mayer notes , Yahoo has changed its logo. It's no massive overhaul, though: "We wanted a logo that stayed true to our roots (whimsical, purple, with an exclamation point) yet embraced the evolution of our products," writes chief marketing...