Perhaps I'm a Killer DM (well, I'm quite sure that the players would vote for that).
In one campaign, 8 PCs died, mostly because of stupidity, heroism (yes, it sometimes happens

) or because they didn't get the hint to flee a lost fight...
The other campaign, ToE, has seen six dead PCs so far...the split-up tactic is a bad choice in a shadow-infested area, as well as fighting a demon alone (which is some sort of suicide) or ignoring the warning that a banshee is very close. The last kill: our priest of Lathander was burnt to ashes by a red dragon's fiery breath...(because he forgot to cast
Fire Shield before attacking the dragon)
If the players are smart (at least a bit), develop a reasonable plan or do something unexpected (but not foolish), risk of death is quite low. I dislike save-or-die situations, if they occur, the group gets a hint of how to avoid them (through role-playing, of course). A failed save is always bitter, but that's not in the hands of the DM.
As a player, I'd like to develop the PC and the story. Victory is not that important, but always losing or being on the edge of destruction isn't fun either...