I roll 120hz and the difference is noticeable. Rocking Crysis 3 on maximum settings at 120fps is quite something.
Having said that, it isn't really that important to me these days. I'm perfectly happy playing Destiny at 30fps on PS4. In fact in some ways it's better. Certainly feels more cinematic. But yes, if you're living by the 'frames for life' power PC ethos, then 120hz (I haven't tried 144) is a marked improvement over 60, and the buttery smoothness adds extra realism unless your eyes see RL at 30fps.