We haven't had any deaths in the 1 16-level campaign I've been in, the short 3-level campaign I ran, the 2 adventures of Scales of War we've played, or the new 2-session-old game I'm running now. There are alot of times where it was close though:
In the short game I ran, there was one player 3hp from negative bloodied with 5 ongoing damage and two failed death saves. Someone ran up and dumped a healing potion down his throat right before his turn(when he would have died). Everyone ended the fight bloodied with ongoing damage and no heals left.
In the 16-level game, we've had surprisingly few near-death experiences, partially due to some exceptional rolled stats, having a kick-ass dedicated healing cleric, and having solid group tactics. The few close calls I can remember:
At level 3, the four of us "aggro'd" a whole dungeon at once, taking on 3 encounters at once:
8 level 3 skirmishers(Orcus cultists) + 2 level 3 artillery(filth-thrower zombies).
Everyone was down at some point rolling death-saves, and our DM later told us that that was the first time he'd fudged his rolls running 4e. We told him not to fudge again, so it was also the last time.
Around level 4 - 6(don't remember exactly), we were assaulting a wall built across a pass on our way to destroy a pair of massive towers dedicated to Orcus. There were 4 crossbowmen atop the wall and two of those Hulking Zombies or whatever they're called (the large ones) chained out front. While the ranger, rogue, and cleric were fighting the Hulks (one of which critted the rogue and took him from full health to unconscious in one hit), the warlock decides he's going to teleport on top of the wall to kill the crossbowmen.
Unfortunately for him, turns out the "crossbowmen" were actually "halberders" using their weak ranged attacks until we got up to the wall and they could bust out their good attacks. The warlock was at two failed death saves, lying out of sight behind a parapet before the rest of us dispatched the last of the hulks and approached the wall.
One of the halberdiers picked up the warlock and said he'd kill him if we got any closer(action readied to attack if anyone attacked him). Our cleric, now able to see him, promptly healed the warlock, who, on his turn, teleported back off of the wall to safety.
Much later in the game(level 11 or so), our (newly joined) fighter and paladin turned to stone by the four basilisks we were fighting.
The fight before that, we were ambushed by 9 Dragonspawn who all dropped their encounter ranged Burst firebreath attack on us... 9 encounter-level attacks on each of our 5 PCs...
Due to some poor rolling, most of us were "only" hit by 4-5 attacks, bloodying all of us except the cleric who was hit by 7, taking him near negative bloodied. What the DM had missed (and only noticed after the fight was over) was that the Dragonspawn should have done 1/2 damage on a miss, killing the cleric outright and dropping a few more of us. So, that should have been an instakill - and quite possibly a TPK without the cleric to nova-heal everyone up.
In my new campaign I'm running, they've only had 5 combats so far, 4 of which had at least 1 player unconscious making death saves at one point or another.
In one fight, they stumbled into a natural trap - hallucination gas leaking from the ground - that attacked them every round and made them think all the other players were demons until they saved. Fortunately, the swordmage made a couple saves and got out of the trap area, noticed it wasn't magical, and held his breath on a hunch. Two of the players were on their second death saves before they managed to get them all out. In a side note, in player-versus-player free-for-alls, it's tough to beat a leader. The bard and warlord were the last two standing and the warlord was the last one, landing the "dropping blows" on nearly every other player.
The last fight - trying to disrupt a town full of cultists from opening a rift to the abyss - everyone went unconscious at least once except the swordmage(who was busy counter-ritualling the high cultist to control the rift for most of the fight).
Not terribly surprising that they had a hard time since they, at level 3, were taking on:
40 level 1 minions
1 level 4 controller
1 level 4 soldier
1 level 4 solo artillery
Skill challenge: magical barriers and a rift to the abyss(with the potential of releasing additional minion demons and eventually a Gnarled Demon(level 5 brute) into the fight.
All the bard's heals, every healing potion, and every second wind was used. If it weren't for the bard planting a Battle Standard of Healing at the beginning of the fight, they'd never have made it.