I worked mainly for privately held companies where you would still find a significant portion of the employee being in the company more than 20 years. Although I would value their knowledge of the unwritten rules and ability to get things done, I must say that a lot of them would develop a sweet-bitter attitude over the years, with a tendency to look at the past with excessive nostalgia. I think it is perfectly fine to be loyal to your company while still having changes in your career on a periodic basis. Each time you move, it creates a bit of chaos that would ultimately benefit to yourself as well as your prior employer. Life is about changes… but this is just my personal feeling towards changes in life !