I used to work at UPS and they force everyone to unionize, and some still got crappy pay and benefits, nor did the union do anything to protect the workers. they got fired just as easily as everyone else, if the pacage delivery guys were too slow delivering packages 1 day they could get demoted easily and get in trouble if they get in a accident even if its not their fault .
I have never had a manager at FedEx scream in my face or mistreat me in any way. There is a very definite list of things that you can be fired for ("Falsification" being the chief reason). I did receive disciplinary action for having too many late deliveries one day, though; and three of these actions within a twelve-month span can result in termination.
The benefits certainly aren't as good as when I started 5 years ago. Back then, individual health insurance was totally paid for by the company. Family plans ran to around $90 a month. Up until 9/11, employees could jump seat to anywhere FedEx flew (I got hired too late to enjoy that benefit).
Accidents are a ticky thing; you can't really get fired, but they kick up a fuss in management. A lady ran a stop sign one day and hit me; the accident review board (or whatever they're called) came to the conclusion that it was my fault; I should have waited at the stop sign to see if she were going to come to a complete stop before I proceeded through the intersection. I had to go to courier re-training class for a week. Which reminds me: if a FedEx guy honks at you, it's probably because he has a courier trainer riding with him. It's part of the training to honk at people to make sure they see you.
Still, it's not a bad company to work for; I've worked at worse jobs.