Well, sciforums is known to have arranged the odd Ph.D. waving contest, however this year, no clear winner was declared.
Not always... for example, Adam Spencer is a stand-up comedian and radio breakfast show host. That's where a PhD in Maths could take you!
I have (once I do a few corrections) a PhD in theoretical physics, in an area which everyone else in the physics department I'm in considers to be pure mathematics. Ben has a PhD in theoretical physics. Prometheus is working towards one. Guest has a PhD in mathematics. And I'm pretty sure DH has one in some mathematical or physical area.