Most of the "storytelling" in Left 4 Dead takes the form of messages scrawled on the walls of key locations, as desperate survivors left messages for each other while they fled the zombie horde. When I see these I can't help but think of what the walls would look like if players could leave enduring messages for each other.
Actually, I think it would be a lot worse than what I depicted to the left, because halfway through the thread some ass would have come in and simply colored in the entire wall in black magic marker.
I reflect on this whenever I cause a friendly fire incident, and then I don't feel so bad about it.
Shamus Young is a programmer and writer by trade, videogame nitpicker by inclination. If you have the patience for more of his ramblings, they can be found at ShamusYoung.com.