Well, shaving 5 lbs from a bike might be a bit counterproductive. Bikes are made for a certain suite of components. Does it make sense to run really light and expensive components like ultra high end wheels and tires and have dirt cheap, clunky brakes? Why stick $1000 of wheels on a $600 bike?

I think if you want to go for a light ride, just go and get a whole new bike. Use your old ride for a back up and a beater (rain, bad roads, nasty conditions).