Same with mechanical keyboards, once you go 120Hz you never go back.
Personal opinion, but I can tell a 120Hz screen from a 60Hz any day of the week.
I think 120hz is a good feature.. but the lightboost imo is what you should be after.
it flashes the backlight of the panel @ 120hz or 60hz.. this removes some of the perceived motion blur inherent in lcd panels..
This essentially inserts a black frame between each lit-frame..
The lightboost and 120hz are good for MOTION...
However, the trade off is, very bad color reproduction.. and since it's TN, theres the viewing angle problem compounded by the usual lack in luminance uniformity in this genre.
Still.. if you play FPS games.. It's stupid to play them on 60hz ips when you can get 120hz lightboosted tn panels..