That pretty much mirrors my own experience. I've been playing PC shooters since ...whatever day one was. Throw in some Atari ST/Amiga mouse use before that. That's well over 30 years of muscle memory.
I resisted getting a console as long as I could. I even played the first 2 Halo's on PC. But then in 2006 I moved, got a new job, then discovered some of the guys I worked with had a weekly game night where they got together on the Xbox360 and played L4D, GRAW, and so on. So I bit the bullet and got one.
And immediately discovered that I suuuuuuck with a controller. I couldn't understand why you couldn't just plug in a mouse & kb, why they would limit it like that. Still don't, really. But rather than give up or be frustrated all the time, I found Xim.
We play co-op most of the time, but occasionally when we do play PVP I don't 'kick everyones @#$%', rather the reverse. So if any of you console makers are reading this, you can count me among one of Obsiv's 'people who use it not to be disadvantaged', and know that banning keyboard and mouse would probably result in this 51 year old guy hesitate to ever buy another console.
Also, I am of the opinion that if the controller your opponent uses makes or breaks your game, then you need to work on your tactics. It's definitely my problem in PvP