There have been some interesting ideas put forward. I've latched on to one question though - how deadly should any individual encounter be?
I guess the question here is - how many will there be in a typical gaming session, and how long do they take?
If a combat is a 5 minute affair, then it probably shouldn't be very deadly. If a combat is 1 hour, it probably should, otherwise there is no real tension.
If you want to do 20 combats in a session, the combats can't all be life-or-death situations really, and both the number and the expected deadliness point to short combats. Combat becomes something that may be abit more elaborate then disabling a trap.
If you want only one combat per session it can be deadly or easy, but it probably depends on its significance and length whether it's supposd to be deadly, but again, the longer that combat is too last, the more tension it must offer, and that probably requires deadliness.
3E with its CLW Wands caused a situation where you really wanted combat to be deadly each time. BUt the rest of the system wasn't prepared for that. Your spell swould run out so fast (and spellcasters would both be needed and dominate for that to work.)
4E ran with that concept and ensured that hit points would go up and down a lot and significantly so - you would go bloodied and close to 0 if not below quite often, even if a healer was present. Every class had healing surges and daily powers to deal with that, so no class could really dominate, and everyone was challenged to bring his best.
I enjoyed that, but 4E did kinda remove the "easy" and "short" combats. There was a reasonable chance no resources at all would be spent in such a combat, and the combat would still last too long thanks to the variety of options and the hit points the NPCs would have (and if you'd use minions, the combat could be over after the first area attack, several of which only being at-wills or encounte rpowers).
I thin kfor long combats to be tenseful and engaging, they need a threat of death. In a game with ablative hit points like D&D, that requires a lot of yo-yoing the health - which in turn means mid-combat healing. Otherwise you plink away hit points for so long and pressure is only felt at the very end, if at all (or desperation sets in as the statistics of the situation already tell you're gonna fail, at least if you can't escape the entire fight.).