That was another thing I was worried about, the concept of lethality for characters. During playtesting, there were no PC deaths outside of a TPK caused by the players being entirely reckless during the first session, but every other session things got pretty close, pretty quickly. Things got especially close while testing the Steampunk setting, since firearms not only pack an extra punch in terms of raw damage, but they make armor next to useless. I think the biggest reason that players survived, though, was because they happened to eliminate the enemies before they themselves were eliminated.
I think I want PC lethality to be where it was (in my experience, at least) in DnD 4.0, where, barring stupidity, you can fairly reasonably expect to keep a character for a long time. I could, of course, make house rules to make things riskier for PC's, but I would want the default game to be less lethal per round. The issue remains, however, in how exactly to implement this mechanically.
The easiest thing to do would be to simply increase HP. However, I think it would be a bit intimidating or confusing for new players, especially ones used to other systems, to have a level 1 wizard with no investment in durability sporting 36 HP. Decreasing damage would be much harder, since you can only decrease die size or dice rolled so much.