I don't want to discourage anyone from pursuing a JD, but my advice is to do so only if you are serious about practicing law (and maybe if you are interested in public policy or working in the government). I am not convinced that a JD/MBA degree itself is all that helpful to folks who want to stay in business and have no interest in practicing law. I do think it is useful for attorneys who want a comfort zone with business concepts.
What a JD alone will not do is make you a go-to guy in your business firm for legal issues. Basically a JD without experience in a particular field is, well, kinda useless.
What a JD will do is teach you to spot legal issues and problems, develop your analytical thinking ability, provide a framework for understanding the regulatory system within which businesses operate, and hopefully improve your communication skills.
My sense of law school v. business school is that both are demanding on your time, but in different ways. Law school time consumption to me was mostly class +
massive reading (and I mean alot). Journal work and job search were in there as well. Business school seems like it will also be very demanding on my time but more in the vein of juggling a lot more things of closer to equal time demands.
To give one view of law school v. another professional school, in this case medical school. An attorney in my firm was a neurosurgeon for 12 years before going to law school. I once asked him which was harder law school or medical school. He emphatically replied, law school. I asked why, and he said both required a lot of reading, but in medical school the reading involved a lot of brute memorization which he found easy. Whereas in law school, not only was there a huge volume of reading, but the material (court opinions) was often conceptually difficult and ambiguous. That's was just his experience. It might not have been others.
In law school, you read court opinions to pick them apart, critique the reasoning, and to a surprising degree for me, not necessarily to learn the holding in the case (ie law). I recall being really frustrated spending hours digesting a case, a whole class period arguing over the reasoning of the decision, only to be told at the end of the class that the case hasn't been good law for, say, 100 years. Argh! I suspect every law student has had that experience. It's just the school teaching you to think like a lawyer, not necessarily to teach you the law. Thats what the bar exam is for in their minds.
As a side note, you can get so involved in the reasoning of a case that is easy to lose sight of things that should be obvious. We'd discuss a case all class and at the end the professor would ask, "So, who won this case. The plaintiff or the defendant?" No one would know. We'd all scramble back through the case trying to figure out who actually won. Somehow it got lost in the shuffle.
PS One final thing. I lived with business students when I was in law school and had a lot of friends from that school (an M7). They were - almost without exception - happier with the experience of business school than my law student colleagues were about their law school experience. Law school is sorta of a loner's game. A lot of time is necessarily spent reading and outlining alone. Business school was, even back then, a much more people-centered, team oriented approach (and that business school is not a notoriously team oriented place), and I think that approach lends itself to much happier students. At least thats what Im hoping!