I pulled punches with my players for the first year or so after we switched to 3rd edition. None of us had played anything in a while, we had several new players, etc. I stopped bothering, though. They're big boys and girls. They can take it. I don't try and kill them, and generally if they bite it, they made bad rolls or did something stupid. I actually hate to let PCs die from bad rolling, though. I try and help them out, there, but sometime...
For example, last D&D campaign we ran, party was about 3/4 of the way through a dungeon full of undead & aberrations. Only the last fight is more than 1 CR past their average party level. The rogue refuses to scout, though, so they all get nailed with a chain-lightning trap because he didn't bother to take Disable Device or tell anyone abou that before they got down there (we started mid-level and the first few adventures were outdoors). So, there go some resources. Do they stop? Rest? Retreat? Nope. Okay.
A few rooms & easy fights later, the rogue still won't scout, so the dwarf barbarian winds up springing the collapsing wall trap behind himself, trapping the other pcs in a room with a chaos beast. They'd have slaughtered the thing whole-sale w/ the barbarian & they managed to take it down, but not before the ranger falls prey to that nasty attack. Oops, you use charisma as a dump stat. Well, you'd best high-tail it to someone who can fix that (good knowledge dungeoneering check or somesuch followed by spellcraft told them what was happening & what would fix it). Oh, you want to keep going into the boss fight first? Your call. Good job, you beat the nasty vampire. Too bad you're a chaos beast now.
*sigh*
Z