Pros
Liberty Mutual has great benefits, the medical coverage is good. You get 3 weeks of vacation the first year, plus 4 personal holidays. The hours you work are generally flexible, most departments (depending on the job) will allow you to come in whenever you want, as long as you work a full day. After a year with the company, they will pay for you to go to school for anything to get your bachelor's degree and something business related to get a masters. The people I work with are a great group of people, very friendly and fun to be around both inside and outside work.
Cons
Some of the downsides are getting into the company. For some people, it can be difficult to even get an interview unless you know someone with in the company who can recommend you, or unless you have something that significantly sets you apart from the crowd. Also, depending on the department, it can be that way with promotions as well. Sometimes promotions are done based on merit, and not posted as a new job, so you get promoted based on if management feels you are ready based on what they've seen you do. After a certain grade level, if you do not have a bachelor's degree, it can be very difficult to move up as well.