From my extensive Halo 2 split screen experience I can tell you people go through 3 stages.
1. Starting out and learning the controls in which they focus on there own screen and do not have time to screen cheat.
2. Getting into it and screen cheating like crazy as they use their map knowledge to their advantage. Even when trying not to do it, they will occasionally do it just to check the positions of people.
3. Your get good enough that it is more fun to just play the game then cheat. It is at this stage that you develop a hatred of screen-cheaters. Since I consider myself to be at this stage, yes I hate screen-cheaters.
Btw I call it screen-cheating, screen-watching looks queer.