I have experienced the highest level of responsiveness from an OS with BeOS - this is still unsurpassed.
I totally agree. This is what I liked most about BeOS. I find it amazing that with a super fast modern CPU and 4GB RAM I am still able to render my PC unresponsive for a few seconds - in both Windows and Linux!
That NEVER happened with BeOS, even on very poor hardware.
Man I would love to see what a Be-like OS can do on modern hardware.