In my current campaign there have been two times where I've actively fudged to not kill a PC. I have, however, freely let them hit negative numbers all the time, and they've certainly thoguht they were ABOUT to die a couple of times.
Once was at level 4, and the expert/cleric stumbled into a pit trap. He messed up his reflex save and the dice for the spikes came up maximum, which would have dropped him in one hit. I decided that it wouldn't be much fun to be slain not byut he big fights up ahead but by a trap, so I simply dropped him to -4 or something, which forced the other PCs to heal him up and tread a bit more warilly.
A few sessions ago, a level 9 Druid was involved in my "Alternate Plane = Evil Version Of Party" adventure, and tried to use a Flaming Sphere to attack an evil version of the party rogue. Alas, all that fire tripped the Necklace of Fireballs the Rogue was wearing, and after taking a sneak attack it was really likely that the Druid would have been slain. I thought about it for a second, and thought that since it was an evil version of his own ally, he should have realised that if one wore a necklace of fireballs the other's similar looking necklace was the same thing: this was my fault for not giving the right information, and so I told him to instead take a move action to get away from him before firing.
I'm not against killing PCs in general, but in both those cases it was going to be a bit of a flat event if it had: so I decided to cut them some slack. However, my group is level 10 now and that means they're high enough that Death is no longer such a big issue. A player death is theoretically fixable with spells they themselves can cast, so if the Ogre bashes their head in or the half-dragon's ice breath stops their heart, the campaign is not over. I've certainly not pulled my punches in every fight, and have intentionally given them soem quite rough fights which have brought a few people dangerously close to seeing a tunnel with a light at the end.
The next time someone in my campaign suffers a "will die for stupid reason" problem, I'll probably let it happen. Three strikes and all that.
