i would say most of it is placebo, except some manual tranny oils.
redline for me atleast, really does make a difference. the shfting of my manual transmission has improved greatly. with other oils like valvoline synpower or mobil or amsoil first gear was awalys hard to get into when moving slowly, and 3rd and 4th awalys grind a very small bit. when i put redline in and went out for a spin, i was disappointed in that it didnt help at all. then over a course of a few weeks i noticed first gear was easier to shift into, and 3rd and 4th didnt hardly grind at all.
at this point in time first gear can be shifted into as easily as any other, and 3/4 do not grind at all whatso ever. i have no idea why it took redline a few weeks to start working, but the stuff does work.
now as far as engine oils go, when people say their car revs quicker or feels smoother i believe that to be impossible except in some circumstances like a psd using oil without enough antifoaming agents or some other bizarre instance. i could never tell the difference with any brand of oil o viscosity, and i have used most of the brands and all the weights from 0w20 to straight 50. i couldnt tell the diffrernce between supertech and redline honestly when it comes to motor oils.