Many new players are trying DDO right now, and among their first guides to gameplay are the character creation descriptions. Those descriptions say that Rogues and Rangers can function as scouts for the rest of the party. So what happens? The player is sneaking along happily scouting, occasionally struggling with the party to be patient and let him do it, when he touches a scripted trigger, a door closes behind him, and 15 monsters jump out to eat him while the rest of the group watches (and laughs).
It's almost as if the quest designer wanted to explicitly punish players for trying to scout, and instead reward running together in a tight mob. Some of the quests involving this feature are Taming the Flames, Delera's Tomb, VON5, Wizard-king, Black Mausoleum, and Ritual Sacrifice. Note that those ambushes/lockouts can only be a surprise once, and if any party member has been there before he can warn everyone else. It would be nice if new players had an in-game way to obtain that kind of forknowledge.
Following is a suggestion to improve that situation, although I think it could easily be too much work for the benefit.
New Feature
Add an "ambush marker" map feature to be explicitly added by dungeon designers. When a character whose Spot reaches a set threshold approaches the area, she gets an onscreen warning icon with the message: "You sense that enemies await nearby" or "You feel it would be risky to proceed alone". (The latter message is suppressed if the rest of the party is already nearby)
As an optional embellishment, using the Search skill and passing a set threshold causes visible indications of the approximate positions of the trigger line, gates / forcefields, and monster spawns. It might also mention the monster category (warforged, elf, elemental, etc) in onscreen text.
Complex Option
Optionally, the required Spot threshold could be higher if the character is not in sneak mode or has Hide / Move Silently skills insufficient compared to the Spot / Listen of the corresponding monsters. This would simulate that the enemies hide more carefully if they detect someone coming, and would make stealthy scouting relatively more valuable.