As a program alumni, perhaps I can add my two cents for those thinking about doing the Duke MPP program...either next academic year or in the future. The pros are that it is a small program, which makes it academically rigorous and students can really engage professors on their policy projects/interests. I would say education and environmental policy are the biggies. I had the impression professors won't be interested if you have other policy issues. The MPP/MEM dual degree is very popular. Although a classmate once told me that Nick school students were not as good as MPPs, I personally think you will be well served by having a policy-specific degree. So, think about the MEM. Environmental/energy related jobs will continue to be aplenty in the future.
The cons are that the curricula is somewhat limited. So if you wanted to EXPLORE what you might be interested in BEFORE coming to Duke, tough luck. You want to go to Duke if you know you want to do social policy. Period. The quant training for that is very limited though. Most incoming MPPs have liberal arts degrees, so the math/econometrics is not in high demand...or supply. If you're interested in int'l development policy, Duke is not the place for you either. The PIDP program is not that "meaty" and lacks solid connections with the DC organizations. There is also a Geneva program where people to go UN-type agencies. I spoke with several people and most told me their supervisors there gave them little work, cared little about their interests and very, very few return for jobs in Geneva. The few who do (return to Geneva) get bored fast (that's what a PIDP professor told me anyway). So that program really adds little to starting a career in that industry. My recommendation is to go to Harvard and leverage their many alumni connections in the int'l development field.
If you want to work in the private sector, I'm also sorry to say Duke is not the place for you simply because Duke has very few connections with the private sector. They do, however, have good relationships with federal, state and non-profit type agencies. I've met some alumni that now work in the private sector and most went on to get an MBA or other degree and really didn't have much to say about how Duke helped when they decided to pursue private sector careers. So avoid Duke if you're interested in the private sector. Finally, my roommate was one of the few foreigners in the program and I have to say that Duke offers little support to those folks coming from abroad. I would suggest you pursue an MPP in a bigger, more internationally-oriented program (e.g., Chicago, Georgetown) than at Duke.
In sum, Duke is a solid niche program for those who have a clear idea of what they want to do. But, again, I wouldn't recommend it to everyone. Good luck to all and hope you make a good decision...