I'm curious as well. Although I can't answer your question directly as I am not there yet (in a dual degree program like those you mentioned), I have found a couple articles that deal specifically with JD/PhD career options. One of them also goes into perspectives from grad students in those programs. The only probelm is that the articles are quite dated. I've been looking for newer info since a few weeks ago but honestly I haven't really put that much effort into it. See below.
Hafemeister, T. L., Ogloff, J. R. P., & Small, M. A. (1990). Training and careers in law and psychology: The perspective of students and graduates of dual degree programs.
Behavioral Sciences and the Law, 8, 263-283.
Tomkins, A. J., & Ogloff, J. R. P. (1990). Training and career options in psychology and law.
Behavioral Sciences and the Law, 8, 205-216.
From what I gathered from these articles (keep in mind they were published in 1990), initial jobs that you get with a JD/PhD (or JD/PsyD) will usually require you to focus on one of the other, law or psychology. Later, you can begin to use them in a more balanced manner. Later in your career, the fact that you have a double doctorate helps quite a bit, but just out of grad school that's not as much the case. Below is the link to the American Law-Psychology Society job listings page (you may have seen this already) is a sample of what's out there. See link below.
http://www.unl.edu/ap-ls/jobs.htm
I'm not sure about the other combinations, but you might be able look on the websites of schools that offer those programs and find email addresses of grad students or contact people for the programs who may be able to share their plans or insights. I hope someone else on the forum has more info as I'm curious, too.