Hardware.info decided to conduct a controlled test with 60Hz and 120Hz displays to discover whether gamers are able to discern the difference. A total of 50 gamers participated in the blind test, and afterwards each of them was asked to describe their gaming experience, without being told what refresh rate they had been gaming with.
The test shows that there really is a big difference in user experience between a 60Hz and a 120Hz display as an overwhelming majority of 43 out of the 50 participants (86 percent) picked the 120Hz screen as superior. Interestingly, several of the seven gamers that prefered the 60Hz screen claimed they had achieved a higher kill-ratio on the 60Hz screen. You can read the full report over here.
In the end, 43 out of the 50 participants (86%) indicated in the questionnaire that they preferred gaming on a 120 Hz monitor. Several of the seven gamers that said otherwise used the justification that they had achieved a higher kill-ratio on the 60 Hz screen. The people who did prefer 120 Hz, tended to call the experience smoother and more fluid. Many also noticed fewer instances of tearing, described in a number of different ways.
86 percent is a pretty convincing majority, so it's clear that there really is a difference in user experience. 44 out 50 participants correctly identified the monitor they were gaming on as either 60 Hz or 120 Hz, so apparently it's a pretty visible difference as well.
The people that incorrectly identified their monitors are not the same as the ones that said they preferred 60 Hz monitors. Out of those seven, four did correctly ID the screens.