UPDATE: Franken explains at his site:
No matter how hard we tried, Bill O'Reilly wouldn't sue us. Since that was the whole point of the name "The O'Franken Factor" - to get sued by O'Reilly - we have decided the time has come to change it.
And yet, the O'Franken Factor has, as a title, had its limitations; its own natural life span. It has not, by itself, infuriated Rush Limbaugh nor has it aggravated President Bush. We have been forced to rely on the internal program content to do that. And while we considered adopting the new name "The O'Limbaugh Factor" or "The O'President Bush Factor," somehow they didn't have quite the same ring to them.
So, today, we will mark the program's continuing evolution by taking the nom de guerre, "The Al Franken Show." We have no longer linked our fate with the declining fortunes of Bill O'Reilly. We will not be dragged down with him.