the hand eye coordination for gamepads is more of a platfomer/shooter type game. I don't think there's any major challenge when it comes to FPS.
I said that KB&M is better for FPS, just that I sometimes prefer the gamepad. My reasoning for this was not because of aiming, but because of games with certain mechanics that allow various moves and secondary skills. too much of these leads to odd key mapping and uncomfortable/awkward positioning.
the main benefit for KB&M is how precisely and quickly you can aim--camera movement is also much better, in general. movement is almost negligible as wsad works fine (though I prefer sticks for this), and shortcuts for item slots using the numbers or f keys are much faster.
despite all of that, I often find myself preferring a gamepad in certain games--and far more friendly in those with a complex area of skills.
also bear in mind that I generally dislike FPS--it is my least favorite genre as they are almost all identical, with minor tweaks here and there.
though I am thoroughly enjoying borderlands right now. If only it had a 3rd person view.