my tuppence in response to a few of the above ...
scratch on alloy frame. I've always been led to believe a scratch on aluminium eventually manifests itself into a break (??)
went right off titanium a couple of years ago after there was a lengthy thread on litespeeds breaking behind the headtube. Contributors ended up dubbing them shitespeeds. Did think about budget titaniums from setavento, van nick and East europe, but to be honest, dont like the raw, paintless finish.
carbon - once heard a carbon roadbike break in a race. It was literally like a gunshot. the rider was staggered and fortunately unhurt. He felt nothing give - one minute sprinting, the next standing.
saw roger hammonds bike after the tour of britain finished in our town a few years ago. The carbon forks had big chunks hammered out of it and he had just descended holme moss at 50mph +, so not sure if this confirms carbon's durability, or skinflint management.
Ive got a compact alloy roadbike and a steel "relaxed racer" with mudguards. The alloy is great for an evening bash - light, stiff and efficient, but crap for 3hrs + clubruns, as its too stiff and kills my back and arms. So I prefer the steel bike for sundays. The next summer bike I get will probably 853 steel.