I have to say I thought I'd be substantially better with M&KB but so far I am not. I do have to adjust because the sensitivity and aim is a ton faster than with the controller.
When you bring up the sights in MW2 it goes a lot slower but I think thats a thing with the game and not the mouse. I am also playing on hardcore so without the crosshair I dont always bring up the sights when I am overtop of the enemy and lose my speed advantage a touch.
All in all I still did well, was first on my team a bunch and always had more kills than deaths.
I will try a few other games this weekend if I get a chance and see how they work.