Think its exactly the same as in cod 4. Move to the side and then back, when the little white markers on you screen are about to drop you shoot. Steady aim makes things a whole lot easier. I find the intervention is the best, very good accuracy on it.
I agree MW2 is a lot harder to no scope because there is not damage boost from the ACOG scope lol. But i do get the occasional one with the intervention but it will be pure luck
MW2 is harder, its different, i think its coz in COD4 you had to shoot a bit in front of the person if hes running, but in MW2 you just shoot him direct
yeah its a big step up. personally i just use steady aim for those moments where an enemy pops around the corner and you cant scope. i gave up and i pretty much quick-scope now.
And a HINT for quick-scoping (lots of people will know this):
But when you get Sleight Of Hand PRO you achieve the ability to scope in faster making quickscopes easier and faster.