I have a 120hz monitor on my gaming pc. I am getting rid of it (sticking it in the closet) and looking for an ips monitor.
I also have a 30 inch ips panel on my non-gaming pc that I've hooked up to the gaming one on occasion. But it's too big.
Anyway the plus side of the 120hz is less input lag and better motion, but I only notice this while shaking windows on the desktop, never in games. The 120hz monitor is TN which means the colors aren't so good and it has a limited viewing angle.
Unless you are competitive at first person shooters (wired mouse, etc...) go with an IPS. Just make sure to get one that has low input lag like the dell u2412m.
3d tech is changing too quickly to justify the prices they are charging. It should be $20 extra, not $200