Guess I'm lucky--I jumped bikes every 2-3 years at first, but have stuck with my current bike for 5 1/2 years now and still love to get it out for a ride. Having kids cut my saddle time the last couple years, but I did long trips when I could, and fabricated some for the sake of spending time on the bike--I've rode to a business meeting in Oak Ridge, TN and commute whenever I'm not on daycare drop-off duty. I even still turn to look at the bike when walking away (cue: awwwwww...).
Not that I wouldn't like to augment my current bike with a good off-roader, a true sportbike or hooligan bike, and a sidehack, but that won't happen anytime soon.