When playing in single player mode I find my AI controlled teammates to be reliable and efficient most of the time.
Not prone to making mistakes....err most of the time.

Last night in one of the add-on campaigns I downloaded, we were climbing up the stairs to the top of a tower.
We were looking for any supplies we can get, not finding any we proceeded to
go back down the stairs.
It was nightime and dark, and one of my teammates (Nick) fell of the stairs and plummeted to his death.

Found him at the foot of the tower.
At least he left a good looking corpse.
Makes me feel not so bad about myself, especially when I think of the times
I fell off a ledge, landed in the water and drowned, and a couple of near disasters where I did fall into the water and had to be rescued by teammates.