I typically keep mine for a long time once I find the one that I like. I still have my GT mtb from 1994. In 2015 I finally broke down and bought a new 29er. I still have the old mtb but I have converted it to a rigid hybrid as I still love it. I rode my first road bike for 2 years and got a new one because I figured out what I really wanted. I do not see getting another one anytime in the next 5 years or more. I am seriously brand loyal once I get attached and like to stick with it for a long time. I would have stayed with GT even for the road if it was the same company but it is clearly not. I went to Felt and ultimately Colnago, where I think I will stay.
Do others stay brand loyal and keep their bikes for a long time as well? (I also get attached to my cars and drive them until they become unreliable. I can't say the same for my wife though.)