Pros
If you're in an admin job, you'll be part of HUCTW, which is great. It means a guaranteed 3.5 percent raise, super comprehensive health benefits (very low monthly premium for 100% coverage, you'll never see a bill), and basically job security for life. Not the most time off in the world, but more than you'll find in the private sector (not as much as other institutions like NYU or Big Ten Schools though). If you're in an exempt role, not as cushy of benefits/job security, but you'll get more time off. Huge pro: employees can take classes for free.
Cons
Harvard can be a great place or horrible place to work. The workplace culture largely dependent on the school/center/division you work for, since Harvard is so decentralized. The Harvard Business School runs a tight ship. People who work there often burn out after a couple of years then run away, but usually have results to put on their resumé. The med school/school of public health are very low key, casual. The Law School and Kennedy School are high pressure but people are pretty reasonable (which is not the case at HBS). Although they can feel like Mad Men at times due to annoyingly persistent gender roles (lots of pretty blonde girls supporting old white men). The Harvard Extension School/Division of Continuing Education are a sinking ship and I've never met anyone who liked working there - I highly advise against that. Other con: it takes 3 years for your retirement to be vested, also can be very difficult to grow/be promoted. Too often people are "promoted" to a job that pays exactly the same. Lastly, it can be frustrating place to work due to Harvard's obsession with good press. Harvard is at the forefront of knowledge, with more money than other university in the world. They should be taking risks everyday, but Harvard's senior leadership is too focused on maintaining a positive image and decreasing any kind of risk to ever let that happen, which is truly a shame.