If you are nearing 55, be ready to be shown the door. Shell Oil regularly uses layoffs to get rid of older workers it pays more and replace them with younger, cheaper workers. Of course, they add a few younger folks into the mix to make sure they avoid any possible ageism claims or suits.
Even before, in your late forties to early fifties you'll be able to see this play out in more moderate form. You might find yourself passed over for a promotion, or downgraded from a managerial position back to technical.
This is really hurting the company in the long run - you can't simply lose all that experience and knowledge, replace it with a bunch of greenhorns, and then expect to continue as usual.
Oh, and before I forget, getting on manager's bad side guarantees that the next layoffs round will have your name on the list. No matter if your grievance was legitimate, HR will stand behind the manager, who will then use the first possible opportunity to get back at you. I have seen this play out more times than I can say.