Let the dice fall where they may...and I roll them in the open so there is no screaming at the DM...just scream at the dice.
Seriously, once you start ignoring die rolls or fudging them the dice lose validity. The entire conflict resolution part of the system disintegrates. Those of you who protect the PCs from die rolls are slowly teaching them that they can overcome opponents that they shouldn't be able to overcome on a regular basis. This, in turn, leads to the DM cornering himself as the PCs become more and more brazen in their approach. Smash-door becomes the status quo tactic for the group.
Then when you want to tighten the game back down again the players think you're being overly harsh. So now you're the bad guy/gal because you were trying to be nice. It just isn't worth it. Let the dice fall where they may and encourage the players to be creative in their tactics and careful on who or what they face in combat. Knowing that the dice are very real and that the result of a conflict may include PC failure (including death) raises the level of dramatic tension. It is in that same tension that the very best moments of gaming are to be found; whether the conflict is combat or social in nature.