Pros
RAND has nice offices a block from the beach in beautiful Santa Monica. On the civilian side, you have very smart researchers working on important problems. On the military side, the research is relatively easy and job security is possible. You can try working on different types of problems and are not tied to any one "boss". Benefits are good and improve the higher in the organization you go (retirement benefits actually increase, in % terms, as your salary increases). There are even some "RAND internal" research funds available. There are smart and fun graduate students and new hires constantly arriving.
Cons
The internal job market means constantly interviewing internally for projects. On the civilian side, you have to cover 100% of your time with grant/contract money, which is a tall order. This might explain why turnover is a little high on this side of the house. The military side is run by several gangs (e.g., the Project Air Force FMEP gang) each of which has a few decision makers that determine the fate of new hires (what projects they work on, when they are allowed to brief a client or lead a project, etc.). These decision makers take care of each other first and play favorites with new hires. (Don't expect to have an important role on a project just because you know the topic better than anyone else at RAND.) The military side doesn't do very interesting or technical research (think resolving the same Army logistics problem several years in a row using a giant spreadsheet). Santa Monica and the surrounding area are very expensive and traffic is bad. The freedom to work from home and the nature of the researchers working here means there is little socializing or community spirit at work