Controllers, compared to mouse and keyboard, suck.
If you play any computer games such as CoD4 online with a control pad, you'll get slaughtered.
Once you get used to mouse and keyboard, you'll understand what I mean, there is just so much more control.
Here's the most commonly mapped keys, or at least the way I map things:
W - forward
S - Backward
A - Move left
D - Move right
Space - Jump
C - Crouch
Q - Go prone
E - Melee (Bash)/Sniper Hold Breath
F - Use
Mouse - Look around/view
Mouse 1 - Fire
Mouse 2 - secondary fire/sniper view
Mouse three (click scroll wheel) - Grenade
There are others of course but that's the basics I use.
Believe me, you're mugging yourself if you use a controller for fps's.
I use a wired X-Box controller on my AMD machine, it's a great piece of kit, but mostly for racing games, never fps's.