Pros
Excellent pay and great benefits. It's a fun job if you don't let the pessimists get to you. UP will be around for a long time. Just find a position that technology won't take sometime in the near future.
Cons
Expect to work shifts/jobs that you don't enjoy for the first 2 -5 years or more, depending on seniority. Many layoffs and cutting other essential resources in order to save money. Expect to pay dues to a Union every month that honestly doesn't do as much as we would all hope. Technology is growing exponentially on the tracks and my educated guess is that it won't be long until UP moves from 2 man crews-->1 man crews-->Trains operating themselves. Unfortunately, when it comes to managers and crews, there isn't much collaboration but rather confrontation and resistance. Front-line managers are usually great to work with but their superiors put a lot of pressure on them to make the impossible happen which is likely due to not really being exposed to the fine details of the actual operation.