Traps seem to serve several different roles in the game. I think they're all useful, but should perhaps be adjusted a bit.
1) Traps as 'gotchas!'. (Example: the party opens a chest to get at the treasure, triggering a poisoned needle.)
Frankly, they tend to be a bit dull, because very quickly the party develops a "standard operating procedure", the Rogue makes two skill rolls, and it's done. (And if the Rogue fails, the Cleric steps in with a healing spell.)
Fixes: These should probably be used sparingly. They should be relatively easy to find, but considerably harder to disarm. And they should be potentially lethal - if the party decide to tough it out, there should be a real chance of a PC being killed outright.
2) Traps as terrain. (Example: the party are fighting kobolds... and there are several hidden pit traps in the room.)
These are great! The party probably won't have opportunity to find or disable these, they provide a useful tactical element when they are found, and they are just fun.
Fixes: Use them more! These traps should probably be easy to find and/or disarm... if the party have a chance to look for them. Ideally, there should be several similar traps in the area, with similar markings (so that, having fallen afoul of one, the clever PCs can then make tactical use of the others). Also, since they're only part of the encounter, they don't need to be particularly lethal.
3) Traps as encounter. (Example: Indy and Short Round get locked in a room with spikes...)
These can also be good, but they tend to be hard to pull off. Basically, the PCs are caught in the trap, and have to disarm it before it kills them.
Fixes: A "Book of Traps" (or a traps section in the Monster Manual) would be useful, providing examples of these things. Encounter traps should be very hard to detect until you're in them, should be disarmed in multiple stages (but with each stage being reasonably easy), and should probably cause an amount of damage per round (rather than a lot all at once). I see no reason why such traps shouldn't be lethal over time... although 4e avoided Skill Challenges with the possibility of death.
4) Traps that move the party. (Example: the party walks along a corridor, not realising they've been teleported to an entirely different part of the dungeon.)
You don't seem to see these very often, but I think they can be fun. Basically, anything that removes the PCs from the 'safety' of a known location and/or makes it harder for them to escape back to safety has the potential to ratchet up the tension.
Fixes: Bring them back! These should probably be very hard to find, but perhaps very easy to disarm once found. There's no particular reason these traps should cause any damage.
One more thing: I'm leaning quite heavily towards the notion that most traps should have clues to their existence scattered around the dungeon (not necessarily by the trap itself). For example, perhaps the PCs find a treasure map with some traps marked (but make it fairly vague, so they still have to work out exactly where it applies!). Likewise, most traps should provide a mechanism for disaming them other than the Rogue rolling his skill. That way, clever players can simply bypass the skill and solve the 'puzzle' automatically (gaining more satisfaction from doing so). Providing an alternative also allows you to increase the Disarm DC, since it's no longer so important whether they succeed or fail.
To a very large extent, though, I'm not sure traps are entirely a rules matter. I'm inclined to think they're more an adventure-design issue - I will be very interested to see how (and if) they're used in the 5e adventure modules.
