Don't do it...

Jay Kaufman sends along a bit from the Economist about the futility of earning a PhD. My favorite part:

One thing many PhD students have in common is dissatisfaction.

But this gets to the heart of the matter:

There is an oversupply of PhDs. Although a doctorate is designed as training for a job in academia, the number of PhD positions is unrelated to the number of job openings. 

And later...

America produced more than 100,000 doctoral degrees between 2005 and 2009. In the same period there were just 16,000 new professorships...
...Even in Canada, where the output of PhD graduates has grown relatively modestly, universities conferred 4,800 doctorate degrees in 2007 but hired just 2,616 new full-time professors.

Wow.

Right now this seems less true in epidemiology (the job market still seems relatively strong), but recent doctorates are still in need of retirements or deaths.