Yeah, this is my experience too, trading up every couple of years (though sometimes I've taken a sideways or slight downwards step to broaden my experience or work for somewhere that I thought was interesting or worthwhile). I've had a couple of longish spells at companies, 7 or 8 years, and in both those cases I left because my pay wasn't keeping pace with the market or my growing responsibilities and management wouldn't budge. The irony being that at those places i was at my most valuable because of my institutional and political knowledge. I think companies greatly undervalue the benefits of long term employees.