We had a "technical" party wipe last week. Only one character survived, and really that was only so the DM would have a way to continue the campaign. He should have died right along with the rest of us.
We were in a kuo-toan temple to rescue a dwarf, and we had just finished off the priests and archers in the main worship area. It was a hard fight and we were all down to less than 20 hit points (at 7th level). After the fight, we stopped to rest and heal up. Well, we didn't have time to do that, for less than 2 minutes after we entered the main worship area, an erinyes appeared and started using multishot on us with her flaming bow.
The warlock was the first to drop. At that point, we got the hint and ran for the doors. We tried to brace the door shut behind us but she broke through. I tried to buy the others time to escape, but she was having none of that. I was dead, and the fighter soon after. The cleric was next. The ranger, whose player was absent that night due to medical reasons, was presumed killed as well. Only the rogue/monk escaped, by using a potion of Gaseous Form to flee across the lake that the temple was sitting in the middle of. Again, he really should have died; the erinyes could have used True Seeing to spot him in the fog and pepper him with arrows.
I don't remember what the DM's excuse was for this slaughter, but the real reason for it was evident--he put too much faith in the adventure designers making each encounter fair and balanced. The erinyes, he said, was CR 9--normally not a problem for a party of five 7th level characters. But this attack came right after a battle with 4 kuo-toan clerics and 4 archer guards, so really it was one big encounter.