Results: 86% prefer 120 Hz!
It became clear pretty fast during the event that most people were able to see the difference between 60 Hz and 120 Hz monitors. In the course of the afternoon there were enough participants that came to the conclusion on their own that it was high time to invest in a 120 Hz display. More than a few only needed a few seconds to say whether they preferred this or the previous monitor.
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.
Almost half of the participants got the refresh rate right for all 12 monitors, despite the fact that each gamer only got to actually use two of them. For the rest they had to observe from a distance. 70 percent got at least half right. The difference between 60 Hz and 120 Hz is most noticeable when you're gaming, but it's clear a lot of people can see the difference just by looking at the screens, so it's not merely a matter of a ' smoother experience'.
For the chart below it should be noted that a few gamers ran out of time, and probably guessed many of the answers.
Then we asked everyone if 120 Hz monitors improved actual gaming results. You can't draw objective conclusions based on just a single session on each type of monitor, but to get an impression we subtracted the number of deaths of each player from the amount of kills. We have the stats for 43 players, the others were lacking one thing or another. Out of the 43, 22 had a better result on 60 Hz, and 21 gamed better on 120 Hz. It would appear it makes no difference based on our test subjects, but a much larger study would be needed to draw real conclusions here.