For real-world riders - that is, everyone except racers with factory bikes - I can't see what the attraction is with bikes made out of aluminium and carbon.
I've got a Cannondale caad9, which I've only kept because of the lifetime warranty. I've never cracked one but when I'll be on my 3rd one soon because of corrosion under the paint. Ok, so it rides great, but I never enjoy using it because I know every pedal revolution brings the bike slowly closer to unavoidable failure.
As well as looking elegant, a rustproofed steel bike can last a lifetime, and you don't have to worry about the bottom bracket shell breaking off. There is no way I will ever own another aluminium bike. And as for composite - I really don't see the attraction at all.