Square taper bottom brackets. There is something great about them; a distinctive feel when you tighten the crank bolt. As the bolt turns, you expect the wrench torque to increase hugely as the bolt seats on the crank, but counteracting force only increases linearly as the crank relents and slides up the tapered axle. After a few more turns the correct foot-pound is reached and you're done.
You can feel the same thing every time you put force on the pedal. Old style cranks and BBs flex like a spring, accepting your energy every stroke, and then giving nearly all the energy back as the pedal follows through. Newer crank/BBs have a strange quasi stiffness: more flex to the frame, and some to the drive train.
I'm in overhaul mode on my bikes. My soon-to-come mountain bike stole my commuter rig's crank and I'm replacing it with this beauty