Get a hammer without padding on the handle (damaged etc) or a metal tool (crowbar) and hit another metal object with it. You feel that instant numbness in the palm of your hand?
Take a bike - it's more cushioned (tires are on the ground) but you can imagine if you hands went instantly numb and tingly as soon as you hit a bump. In fact, you can replicate this - ride a steel bar with no tape. Ride over 50 yards of heavily cracked pavement. Presto! Instant numb hands.
So yes, it's important to absorb or otherwise deflect some of that sharp shock. Aluminum and carbon fiber bars are a huge improvement over steel ones. Ditto forks, seat posts, even stems. As for frames and stuff, that's really debatable since it's impossible to be consistent design-wise from one material to another. However, personally, I think there is a big difference in damping properties of different materials, *as long as they are used correctly*.
The last bit is important. Used to be that aluminum frames (Vitus) were noodles, like limp spaghetti. Now people think of them as original generation Cannondales and say they're too stiff. It's not material, it's design.
cdr
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"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson