For the most part, it does seem more "profitable" to jump companies on a regular basis for the pay increases. A friend doubled his salary in one year by jumping twice, but then again, he's in a high demand position.

I've been lucky enough to stay with a private company for a good chunk of my career and am set for a comfy retirement. I wouldn't mind doubling my salary, but I don't NEED it. Helps to be single with no kids, though.