Okay, I'll give you a bit more than that. Fine. Be that way.
Let me first qualify 'death.' When I say a character is 'dead,' I mean 'unplayable.' I do not mean 'mildly inconvenienced' (hi, Epic Level!) I do not even mean 'significantly inconvenienced' (level loss, etc). I mean 'open up the character builder and start choosing stats.'
As a DM, I have a mixed relationship with inflicting death upon Player Characters. On the one hand, I want people to be responsible for their actions, and for consequences to be realistic. I want there to be a sense of danger in combat, and a thrill when a monster's attack narrowly misses or a key save is made.
On the other, people do not like having their characters die. Players get understandably attached to their characters. They should. If they don't get invested in their characters, the campaign (or at least any 'role playing' therein) is likely to suck. But, of course, this attachment also means that it's difficult for me to kill their beloved characters, even if that's simply how the dice fall. I'm not there to emotionally scar my players, I'm there to have fun with them, after all (though some DMs might take a different stance on the issue of whether or not emotional scarring constitutes fun).
So, historically, I have made compromises. There have been three fatalities during my two campaigns, and none have stuck. I'm not entirely happy about this fact, and while I'd like to rationalize each of my decisions, the fact is that, historically, I've been unwilling to actually take the hard line I espouse in theory on character death.
Monster Power Cards, which clearly define the abilities that monsters have to the players, are one step in the right direction. If monster abilities are more static, I think death seems less arbitrary, and "fairer," even if from all functional standpoints, I still control what abilities the monsters have. Players seem to be more bothered by the DM coming up with something on the spot than with regular unbalanced design, and I'm happy to accomodate this preference. I think the Joker had some good stuff to say about this idea in The Dark Knight.
The 'Table of Messy Results,' which substitutes gross bodily injury for actual death (most of the time), is another helpful tool. Having a character greviously injured provides a challenge to overcome (for the player and the character) as a penalty for failure. It might require a change in direction for a character's development, but I'd say that's a good (or at least interesting) thing.
I also hope that having more experienced players will lead them to accept the results of their actions, and more importantly, lead me to be willing to follow through on those consequences. I hate the thought of being the douchebag DM who turns the newbie's first three characters into bloody stains because he or she happened to be (understandably) genre blind. Yes, many people learned to play this way. Yes, 'back in your day, you didn't have no fancy healing surges. You had 1d4 hit points and a rock. And you had to share the rock.' Yes, I'll get off of your lawn. If it's nobody's first rodeo, though, I think I'd have less pangs of guilt about smacking PCs for making foolhardy, misinformed, or just plain unfortunate decisions.
In the end, though, it really is on me deciding to stand by the ideals I've put forth numerous times on the subject. Anyone have any insight on this? I'm always open to hearing new ideas regarding this tricky subject.