This is a dialog I have with myself all of the time. I want a light bike, a nimble bike, a strong (enough) bike. I want a bike that can deliver more than I can ask of it. And I always ask myself: What difference will 50gms really make? or even 150? or even 450? perhaps in the case of Cervelo. Heck, I vary up to 2 pounds a day, and I have to carry myself up the hill every time I ride. So many people ride with TWO water bottles on their 16lb bikes. Water weighs 8lbs a gallon. One guy on this site said he saves weight on his bike by wearing a camelback! Have you checked out the weight of a camelback? Ooch. Howcome, no-one ever asks what shoes weigh, and no company devulges this info. You've got to haul the shoes up too, don't you?
The other thing thing that strikes me funny is that people focus on rotational weight. Isn't the concept that a force in motion, will remain in mothion. Yes we have to set it into motion first, but the energy is not lost unless you hit the brakes.
None the less, I want a frame under 2.5lbs max. and I bought American Classic 420's to replace my Ksyrium Elites, and I'm looking at lighter components because... in truth I'm addicted to this sport, an looking at it's equiptment and cruising the web in search of more bike info is the closest I can come to riding to fill my obsession until my next ride.