NW JD/
MBA admit here...I'd be happy to answer any specific questions you may have, but to address a few:
1) For me, the LSAT was significantly harder than the GMAT, and I think it requires a lot more practice and preparation than the GMAT. Then again, I'm also more of a math-minded person, and I took the GMAT closer to my college days when my mind was fresh (not old and senile like now

). I did take both, but my LSAT score was so embarrassingly low I did not submit it. It really does depend on the person and their own talents/preparations.
2) Finances is a big concern; these programs are expensive. If you're really concerned about debt, it becomes a bigger concern. For me, the educational experience of both a JD and MBA, and the expected post-grad income (shaky in this economy, I know, but hopefully will be better when we graduate) overcome the debt question. Also, keep in mind that with these two degrees you have two very lucrative job markets open to you, unlike traditional MBA candidates.
3) People love to give opinions about whether a JD/MBA is "worth" it, and usually these opinions are very strong. I'm not really sure why this is the case. It's always a mixed bag, and I would take any admissions consultants' opinion with a grain of salt. (Think about it: if they start advocating JD/MBA programs, they then have to be prepared to advise on JD/MBA programs, which they're probably not qualified to do. Keep in mind most programs are not very integrated and require separate applications to the business and law schools, whose admission processes are VERY different.) Likewise, some JD students and MBA students feel intimidated by those with both degrees and seek to discredit it. Don't listen to these people either. In industry, you will find strong proponents of the two degrees as well as opponents, but it's all up to you on how you portray yourself and your reasoning for the degree. Personally, I've found a lot more supporters and I do think that the dual degree is becoming more and more important in today's world.
In the end, it's about what you want to do post-school and why. I think the JD/MBA is equally lucrative for both business-minded and law-minded people. The big consulting firms, especially McK, love JD/MBAs, and the degree will at least earn you a second glance out of the pile of resumes from top schools. On the flip side, you'll find that as you progress up the ladder in the major law firms, many partners will have MBAs. Firm life, at the end of the day, is all about bringing in business. It helps to have a MBA to do that.