I had wondered about using a modern tv as a monitor for gaming but I've always been told there is way too much input lag. I think I even looked into this within the past few months and it seemed like the answer was still the same thing. Input lag is a big problem when dealing with FPS.
This is also another reason I'd like a monitor running at 120Hz instead of 60Hz.
I never noticed a lag, but I never looked for it. Like I said, I never played much. Although if it was bad. I am sure I would have noticed. But even the lag on my 1.4L doesn't bother me
Disclaimer - It's been a while, and I could be wrong on some things. If I am, sorry in advance. Do your own DD to be sure.
You probably already know a lot of this, but I will post it anyway
There are so many factors. For example, a 60 Hz monitor will only show you 60 FPS, 120Hz, 120 FPS, etc... But a bigger factor is the response times. If it can't change the color of a pixel fast enough, there's ghosting. So, the faster the response time the better. (5ms of less)
On the Computer side, the higher the FPS the better. If that's low, you will see it in slow movements. The CPU or GPU, can't put out fast enough, and the video displays what it has, which is behind where it wants to be.
With a fast CPU or GPU, then the current image gets processed in time and is ready to be passed to the Set. It passes exactly what you want to see at that instant, even if you didn't get to see the past few frames. Some games use the CPU more, some a GPU, so to cover all bases, you want both to be good.
Another factor in how it looks of course is the resolution. I hate the salesmen pushing 720p or 1080i sets, saying it will be OK. It should be 1080p or better to really look good. 720p and 1080i are OK for video, but they aren't good enough for games.
So, as long as you have a frame rate at 60 Hz, and the monitor has a good response time, like 5ms or less, a good CPU and an decent GPU, it should at least look good, without ghosting.
After all that, there's still compatibility issues. Sometimes 120Hz or 240Hz sets don't play well with 60Hz games. Because the 120Hz sets are designed a lot of times for 3D, it means it does extra processing, which could delay the video at times and cause tearing or jitter. I hear the 240Hz are better, but not perfect.
Some sets you can turn the 3D processing off, some you can't.
There are so many other factors that can affect good, smooth play too. Internet issues (if online), Poor Drivers for the video card. etc.....
Also, avoid playing on Plasma TV's Plasmas for gaming are a BAD choice. Even with the ways they shift images, and do other tricks to avoid burn-in, I just think it's plasma's inherent design that's the issue. No fixing that. I've seen a few Plasma's with burn-in. Friend owns a TV shop. Things like the ole ESPN scroller. Awesome pictures for movies though.
I do notice temporary retention in my old LCD, but by the morning it's gone. With a plasma, it's eventually forever....