*sigh*
Let's get up front with the two things that I think are unarguably true.
1) Save or condition effects, and particularly the most famous 'Save or Die', are inarguably a problem in that they bypass hitpoints completely and result in the random death of NPCs (bad, but endurable) and PCs (really bad). While it is true that often times a player who is rolling 'Save or Die' has screwed up, that isn't always true (especially when the save is provoked by an active attack) and no player should lose his character to pure blind bad luck and most especially not a single dice throw.
2) You can't just remove save or condition effects from the game without making it something other than D&D. Literal 'Save or Die' situations are much less rare than, 'Save or Lose' situations. Paralysis, polymorph (including petrification), mental domination, and unconsciousness (including sleep) all basically amount to 'Save or Die' in alot of cases. While this is most true in the case of PC party vs. single powerful NPC (again, bad but endurable), its very often true for the PC's as well. Versus a ghoul pack, the 'Save or be Paralysed' can amount to a save or die in many situations, as the victim is very likely to be Coup de Graced by any DM playing with a reasonable degree of ruthlessness.
There are a variaty of things that can be done about this. One of the more obvious is what 3rd edition did with poison - turn the 'save or die' situation into attribute damage. The problem with this is that attribute damage is essentially maiming the PC, which in terms of game flow may not be an actual improvement. Anyone that has dealt with 3e poison and disease knows that they have a nuisance factor. Unless the attribute damage can be quickly healed, it basically takes either a player out of the game or else calls a 'time out' for the whole party while the character recovers. So, while its a useful solution some of the time, its not a good solution all of the time.
Limitations like 'the spell only works if you have less than X hit points' are clunky, and tend to create wierdness in my opinion. I'd rather that they don't go there.
An alternate approach is the one I have some slender hope that they'll actually take: 'Save or change your condition on the condition track'. This is far superior methodology than anything we've had in D&D before. Unfortunately, I would have thought that they would have leaked hints of a big change like this if it was actually in 4e, and better though it may be than what we have its still very flawed. For example, 'Save or be Dominated' is equivalent to 'save or die' in many cases, and its role in 'save or change your condition on the condition track' isn't obvious.
There is a better solution that uses a tried and proven existing mechanic which I think is balanced and well liked, but I've very little hope that the design team is thinking in the right direction based off what we've seen from Bo9S, SW:SE, IH, etc. Oh well.