Pros
excellent benefits and not just health but within the greater Boston area, discounts to all sorts of things. good intellectual opportunities through lectures and talks and such around campus. the extension school provides an incredible opportunities to get degrees and certificates. Also once you work for Harvard it is much easier to get a different job in a different Harvard school or department.
Cons
poor management. pay inst great. people can be really frustrating to work with. a lot of big egos float around no matter what school or department you are in. Also it is HUGE so it can take a while to get a good understanding of how everything works. Not a lot of feedback or positive reinforcement. My particular job (staff assistant) doesn't require much brain power which most of the time I hate.