Pros
Good pay for a first job, easy to get hired. No interview involved, everyone who shows up is hired. Job is very straight-forward, and you are always busy. UPS is good about promoting from within. If you stomach this job long enough and kick butt you can become a delivery driver.
Cons
Once you get out of the cushy training, you work in the middle of the night (they always have a shortage for this shift). Management is a bunch of monkeys, which is expected at a job like this. Employees are a bunch of monkeys too. Make sure you exercise regularly before working here. I am 6ft 150lb dude. I used to buss tables and I was fast. At this job, I couldn't keep the same pace without hurting my back. I would pop painkillers prior to working, and that would help a lot. While working here a few months my legs would be in a constant state of extreme bruising from the pace they want you to work, so I couldn't wear shorts without looking like a case of domestic violence.