Pros
There is a great deal of money to be made right off the bat. And hours based raises guarantee you will get raises. The benefits package is also very, very good! One of the best I've ever seen, union or non-union. The employee stock ownership plan is also very lucrative if you're with the company long enough.
Cons
The compensation "tops out" around $16/hr. depending on where you work, in a part-time position. The hours based raises do pose a problem if you are very good at your job, because you will make less than incompetent people who happened to get hired first. Can't knock the benefits. Promotions are hard to come by because it is so competitive, and political. All of the supervisiory positions take at least five years to move into and are somewhat based on seniority. This is a very unprofessional environment, just make sure you play the politics and make nice with upper management.