P.J. O'Rourke, Don't Vote
As P.J. O'Rourke observes, famous and infamous, once very different things, have also come a long way toward becoming synonyms. There's a website (crepesofwrath.net) that discusses "the infamous Jacques Torres Chocolate Chip Cookies" in very favorable terms. (I'm not even sure that famous would have been the right word, since I've never heard of these cookies.) A statue of British war hero Sir Barnes Wallis, inventor of the bouncing bomb, carries a plaque saying that his efforts toward winning the war were infamous. In everyday conversation, one hears one word about as much as another, both apparently meaning the same thing.
In fact, they mean something very different. George Washington was famous. Benedict Arnold was infamous. Winston Churchill was famous. Adolf Hitler was infamous. John F. Kennedy was famous. Lee Harvey Oswald was infamous. Infamous means what notorious means. The word implies a bad reputation, not a good one. When President Roosevelt said Dec. 7, 1941, would be "a date which will live in infamy," he didn't mean there would be parties and parades to celebrate the bombing of Pearl Harbor.
The dictionary definition of infamous requires the user of the word to make a value judgment. One has to decide whether someone is famous or infamous. One person might describe George W. Bush as famous, another as infamous. The same with Lady Gaga or Charlie Sheen. It is a word that wise people use sparingly, and never when talking about cookies.