I'm not sure how often people are going to have to explain this but in 4e
you..are...not...safe
we clear on that, just because one dice roll doesn't mean my whole character has just gone down the drain doesn't mean its safe, just because my character can now heal to full health for the majority of time after a fight doesn't mean its safe.
Does it mean 4e is safer than 3e? not in my experience (but then DMs tended not to use save or die effects ever).
You can still die 3 bad saving throws before a heal you're dead, -50% of you're hits past 0 your dead.
If you want more challenging fights in 4e throw a level 5 encounter at the 1st level party each time and you get a good chance of them dying, but a good fight and the party will win.
Well, I am not really clear on that. It sounds like you are saying that where in previous editions, a failed save could kill you, now if you fail multiple saves before you heal yourself, then you are dead. It also sounds like one half the hits you receive after reaching 0 hit points could kill you. Is that true?
First off, save or die is dangerous. Failing 3 saves in a row before you heal yourself isn't so dangerous. It is a case of 'ooohh, I don't really want you to die, roll that again and we'll see if you save this time.' In game I can't really explain it except to say something to the effect of 'great and powerful magic isn't really great or powerful.'
If you don't heal yourself when you can and then take more damage to a point where you die, it isn't dangerous, it is dumb.
Taking damage after reaching 0 hit points should kill you. If someone is damaging your body after you have already been knocked unconcious, then you are dead. Nothing in any edition, at least as far as I remember, tried to alleviate this.
Also, it appears that you said to make fights more challenging to up the enemies power level to four greater than the party. Doesn't that pretty much say that if you continue to give the equivalent level of encounters to the party that there isn't a challenge?
Huh? what? so if a villain didn't have those properties he couldn't kill you, that seems to be what you're saying, surely thats a flaw with the system you are playing, where only save or die can kill you.
Not what I said at all. What I was getting at was if you are facing someone who could kill you with a word, and you succeed, it is much more brag-worthy than running up against anyone who spends minutes or hours whittling you down with little bits of damage over and over again. Okay, maybe that isn't exactly what I said, but it is close to what I mean.

Fair enough I like the idea of getting magical protection but this could very well equate to in 4e a normal challenging wizard but with several higher level spells, the sucessful protection negates him using that and maybe stops him recharging other powers, powers which otherwise would have decimated your party making survival hmm 5-15% likely. Getting magical protection from Miracle Max at the local city would not entertain me, unless it was a sub quest of some importence, just buying it would be utterly pointless.
Wait, you are saying that it would be normal for a DM to create a wizard with a level of power similar to the party, but giving him spells that are way more powerful than the party could get? Is that what you said? The reason I ask is that I saw another thread where someone was mentioning that it shouldn't be a problem giving a low level creature/enemy high level powers if it was just for the encounter or moment.
-wally