First of all, none of the TVs sold in stores are "true" 120 hz. This is because none of them are able to accept 120 hz signal. Instead they take a 60 hz signal and inject frames in to it by refreshing it 120 times.
Rule of thumb - if it's using HDMI it's not able to take 120 hz as for 120 hz you need Dual Link DVI.
As far as true 120 hz displays, they are absolutely awesome for gaming if your rig can support them (PC only for the time being). The reduce the input and visual lag by a half compared to 60 hz input displays (1/120 seconds vs 1/60 second of input lag) and this is really noticeable.
As far as I see it, "faux" 120 hz TV's are a gimmick and waste of money. Get a regular 1080p quality display over a lower brand-model 120/240 hz one. Only LCD's use this technology in order to mask their bad pixel response time. (Plasma or DLP doesn't have or need "120 hz"). However if you can scoop up a real 120 hz monitor for your PC, this is worth investing in to.
Current king is the Asus VG278HE which can accept 144 hz singals
http://www.trustedreviews.com/news/asus-vg278h-is-first-144-hz-monitor-gamers-rejoice







