Pros
Great benefits overall - health, vacation, 401k match, cash pension plan, etc. UPMC has also invested heavily in new technology and, if you are working in that area, you will get exposure to the latest and greatest.
Cons
Large size makes one of the hardest parts of the job managing the size and complexity of the organization, including it's very convoluted and ever-changing management structure and hierarchy. The politics of the place are oppressive. Perhaps not so much so on the clinical side, but for those working in Information Services/IT, it is a constant battle ground. There are plenty of good people here, but unfortunately there are many ruthless ones as well, and all too often the latter get their way at the expense of the company and it's good employees.