Pros
One of the worlds' largest companies--looks great on a resume. One of the few companies that still offers a pension. Benefits are excellent--I'm not aware of any other company (including government) that offers benefits that compare with UPS in terms of cost to employee. Promotion from within can allow people starting in entry-level jobs to advance to senior levels without needing lots of experience or education.
Cons
There is no regard for work/life balance. 24/7/365 environment means that all employees (regardless of department or job function) can work any time, any place, any where. Standard workday is 9.5 hours for all (not including lunch). Career paths within the company almost always involve transfers to various locations and various departments (operations, package delivery, and staff departments).