Pros
The satisfaction of working at a place that does such high quality journalism and music/cultural programming. (You get to listen to NPR all day!) Also, the nature of its "product" makes it an extremely interesting place to work. You learn something every day and you're working with very smart, enthusiastic people who could be working elsewhere and making more money. There's a real dedication to National Public Radio's mission and to quality journalism in every department -- not just the ones actually creating the broadcasts. Folks in human resources or legal, for example, are just as committed to the organization.
Cons
There's a lot of intrafamily squabbling in public broadcasting, which can make it hard to get things done sometimes. You really have to figure out the relationships not just at NPR but at local stations as well. What is good for NPR is not always what's good for local stations and so stations fight NPR quite a bit (they fought NPR having a web site, for example, out of fear that listeners would just listen to NPR programming online instead of tuning into a station. But online, of course, was where media was headed and all they accomplished was painfully delaying the inevitable.)