If you are talking about parabolic zooming, I don't remember it ever being on the official kde 3.x releases. There were some applications that could do it like kooldock or smoothdock, and many others.
But none of them were part of kde 3.x.
They were indeed not too soft in cpu usage. Kde4 has a better infrastructure for these kind of things, but I don't know if plasma support that kind of zooming yet and/or how hard it would be to implement it.
The old panels for kde3 might work under kde4 (provided you have all the needed libs installed). But I don't know how well will they deal with plasma. I am not a big specialist in eye candy.