Pros
It can give great job security over the years of service. Depending on the department you work for, there can be a sense of "family" with working with the same employees and staff. Also if you move to a different city there is the advantage of transfering to another Kaiser, and not losing your senority. They can also offer great medical and dental benefits in this day and age so important.
Cons
Over the years rumors of layoffs or changes seem to always get "leaked" before the official word from management, which is unsettling to those involved. Sometimes changes are made in departments or management that aren't always thought out and end up being changed multiple times during the process. Sometimes upper management loses touch with the front line worker and what is really needed to make things work in the proper setting. Just having a MBA, PHD or years of schooling doesn't mean you actually know how to do a job unless you actually "do the job" and can understand the challenges the effected faces in that situation.