Been using a mouse and keyboard since I can remeber games supporting it and have no problems gaming on a controller. I would not say I could beat out a KB\M user, but I would be willing to play a game with both control sets being used.
What I don't like, is elitist PC gamers that mock the console FPS player (not pointing fingers). Yeah we get it, but we're having fun and the playing field is even in terms of controls. Once you tame your thumb to not move so much and crank the sensitivity, I find the 360 controller quite enjoyable.
Besides, the poor kid with an old ball mouse on his mom's PC vs. Mr. $150 laser mouse with adjustable dpi probably doesn't feel things are going so well.
I would be willing to bet money that a seasoned controller vet could at least provide competition to a KB\M user. Too bad there are no cross platform games worth testing this on.
On topic :
Can't wait for some of these games now that I have a new PC. BF1943, I didn't even know that was coming!!! Good lord I can't wait to play that on my... PC. Bioshock 2, L4D content, I think those will be plenty fun on 360. RTS = nothing but PC for me (although halo wars did a good job on console, if I had no PC and actually thought the game had legs, I would consider it for console).