Yeah, I've had whippy wet-noodle alloy frames like Vitus and the recalled Peugeot Comete. I can flex their bottom-brackets 6" from side to side in a sprint. On the other hand, I've also had the original fat-tube Cannondales (pre 3.0) that were so stiff, my vision would start to get blurry form the pounding ride. Zero flex of any sort. However, on a local 2-mile downhill, I'd be faster on the softer frames which would absorb the bumps as if they had suspension and kept the tyres in contact with the road. On the Cannondale, the super-stiff frame would launch me off the tops of bumps and the tyres would skip like crazy around the corners and threatening to throw me off the cliff.
You can probably create the exact same extremes in "road feel" with any of the other materials as well..
Last edited by DannoXYZ; 01-10-07 at 11:55 AM.