Pros
Free food, laundry, flexible work schedules, commuter shuttles, gym membership discounts, and the opportunity to work with smart & motivated people on a massively popular product are good reasons to work here.
Cons
If you work in User Operations at any level other than Associate or Lead, prepare to be bored, frustrated, and stifled in career development. The jobs in this department mostly involve repetitive task work such as content moderation and responding to user emails, but you will get slightly more interesting tasks from time to time such as working directly with an engineer. You will not be given much respect or appreciation for your work, nor will you be promoted unless you schmooze with the right crowd and embody the essential 'Facebooker'. The bureaucracy problem has gotten much better over time, but it certainly still exists. Everyone is smart, so the competition for a few leadership positions is tough, and you'll be denied promotions for fairly abstract reasons. The target is always moving. It's also quite difficult to transfer to a different department - UO isn't given much benefit of the doubt. It's unfortunate that this department has developed the way it has, because there is a large, untapped pool of brilliant people who could really make great contributions to the product.