Not a doctor, but I lurk here because my wife is a doctor, and I find it a bit comforting to read about medicine and other people going through the same things she does.

Anway, she has always told me that she's glad she didn't marry another doctor because she gets enough medicine at work and doesn't want every aspect of her life to revolve around it. She's also pretty serious and an easily stressed out person, so she says I balance her out since I'm fairly laid back and goofy. For reference, I'm a lawyer, though I work in an in-house consulting position with regular hours, so it's not like we are swinging her internist insanity with big law or whatever.

I think what it really boils down to is how you and your partner, personally, feel about the work/life balance. Some people live for work and want someone else that understands that, while others see work (medicine, law, etc) as a means to an end. Nothing wrong with either way of thinking, but it seems like the real important question is finding a partner that shares the same outlook on how each person's profession influences their life decisions, regardless of what profession that is. Obviously, people in medicine are going to understand exactly what the other person is going through (I only understand now since I've been with my wife since undergrad, so I so everything from medical school rejections, to difficulty in classes, to match day, to boards, residency, and ultimately becoming an attending), but she saw the same for me going through law school, the bar exam, and the job hunt.

I kind of started rambling there, but I guess the bottom line is that the most important thing is trying to empathize with the other person's experiences and help them work through it. Don't need to both be doctors to achieve that.