I know this thread is pretty old, but I figure it can't hurt to respond anyways.....
I'm planning to pursue a JD & MA is Urban and Regional Planning, which is a 4 year course of study, so graduating in 2013. After that I may potentially follow up with a PhD in planning, but I'm just going to wait until I'm done with my masters before making that decision.
I'm interested in going into academia, teaching either in planning schools or law schools or a combination of the two, but if that didn't pan out/I change my mind, I'd definitely to have a job that made use of both degrees... possibly something along the lines of land use law or working for a city's legal department. I can only imagine work using the combination as I find neither law nor planning truly compelling on its own.
The joint degree is definitely affecting which schools I apply to because I have to pick planning programs based on the areas of focus of the professors at the planning schools. I'm looking at UNC, UPenn, UT-Austin, and Columbia for their planning schools, and I'll be applying to their law schools as well (all of which I really like for a number of reasons so it's not like I'm "settling"). I'm also going to apply to Michigan, BC and Yale, all of whom will let me pursue a planning degree at a different university (Michigan has a planning program but it isn't a good fit for me academically). I'm also applying to Berkeley's planning school, which is a great fit, but not their law school, which isn't. Yale, Columbia, Michigan, UT and maybe UPenn are also great because of the extra effort they put into producing academicians, so that was also a factor I considered. Oh, and I'm also applying to Duke because a) I've been in love with that school since Shane Battier was a junior and b) they sent me a fee waiver c) they miiiiiight just let me do a joint degree with UNC and d) I also really love North Carolina.