PC Pros:
Can be graphically superior in every way
Mouse Aiming
Mods
Customisability (not just mods; controls, skins, etc.)
Easy text chat
Can multitask with music n shtuff
Dedicated servers
Steam
Free updates for games that count
PC Cons:
Ludicrously expensive to reach top end (You already pretty much need a computer for every day life, not much of a leap to upgrade to something that can play games well)
Constantly have to upgrade hardware (Only if you feel like being constantly superior)
Occasionally overly complicate controls (Huh? You can edit your controls to suit your needs, over-complication can't really happen)
Compatibility issues
LANing instead of spit screen for local multiplayer (can be a plus)