Louis Menand's The Marketplace of Ideas (http://jseliger.com/2010/01/21/problems-in-the-academy-louis...) discusses time to degree extensively, and the short answer is "yes." The longer answer: I think the average (or median?) time-to-degree for Ph.Ds in the humanities is 9.7 years, while in the sciences it's now hovering around 6 years and trending upwards.

Note that this merely measures the time from start to finish, including breaks.