I think a lot of people are married to their dice.
In both the PBP games I play, and the house games I play, there are invariably players who think that they can just roll dice, get a good result, and should be rewarded.
I prefer just roleplaying a scenario and if as DM I'm on the fence as to whether to give out a given piece of information based on how the roleplaying has worked so far, then I can ask for a skill roll.
I've seen a lot of terrible skill challenges in WotC modules.
I think skill challenges should not be played as encounters, rather they should be played as roleplaying with the players sometimes making a suggestion and the DM sometimes asking for a skill roll for that suggestion.
The mechanical aspects of "I do an Aid Another on Joe's Stealth roll (or Joe's Perception roll or whatever) because I have no skills that are good for this skill challenge" really detrimental to the flow of the game.
And if the DM doesn't allow Aid Another skill rolls for a certain challenge, then the player is still forced (according to the skill challenge rules) to come up with some skill to hack around into something reasonable. That too, to me, is forcing the issue into a direction that I as DM do not necessarily want to handle.
As an example, it's a player's turn in a skill challenge. It is a diplomatic situation and he doesn't have skills like that. So the player says "I use my Acrobatics skill to roll a coin back and forth across my fingers to distract these guys". The player then rolls high on his Acrobatics roll. The player rolled high, so he is expecting that the skill helped and to get a success. As DM, the scenario might be such that I'm slapping myself on the forehead thinking "This is going to tick these guys off because this PC isn't taking them seriously". The player expected the NPCs to be mildly amused or distracted by what he was doing, but as DM, I know that this is not the case.
If the skill challenge rules did not FORCE the player to try SOME skill, he wouldn't have done this off the wall stupid thing and I as DM wouldn't be forced to penalize him for doing it. Now, some DMs would not give him a failure. Other DMs might tell the player that this is not going to work before he even tries. Or another DM might give him a success for trying something unique and the dice roll was good.
But the problem is that the player is scratching his brain, trying to figure out SOMETHING to do, when it is perfectly reasonable for that PC to not do anything. If we would have just roleplayed the scenario, then he probably would not have come up with this lame idea.
On top of that, if we just roleplay the scenario, then the player will often have his PC talk to the NPCs without worrying about Diplomacy rolls. In a diplomatic situation, I want EVERY player talking to the NPCs, not just the one with the highest Diplomacy skill. A skill challenge will encourage players with low Diplomacy (in this type of scenario) to keep their mouths shut in case the DM asks them for a Diplomacy roll which they know will almost always be a failure.
The entire structure of a skill challenge is often backwards from what I as DM want the players to be trying to do. I want them to participate without having to worry about how high their skill modifiers for the PC are.
Another problem with skill challenges is that the players become more concerned with successes vs. failures instead of just going with the flow.
Round one:
Player: "I use Diplomacy to convince him to talk with us".
DM: "I need you to roleplay. What are you saying to him?"
Round two:
Player "Err, I want to use Diplomacy again." (the player not sure if any of his other skills are applicable)
DM: "Again, I need you to roleplay. What are you saying to him?"
Instead of the game just being a conversation between the PCs and the NPCs, it becomes a discussion of which skills to use, rolling dice, and it actually pushes some players away from the roleplaying aspects of it. It becomes more of an out of character meta-game exploration of how to handle the skill challenge instead of an in game roleplaying experience of the encounter itself.
I vastly prefer in character roleplaying with the DM occasionally saying "Joe, give me a Diplomacy roll" or "Joe, give me a History roll" to augment the roleplaying with additional information for the player(s).
I really cannot think of a scenario where either roleplaying with an occasional skill roll, or just a series of skill rolls (everyone rolls Athletics to Climb) doesn't work better than the 4E going around the table rolling the dice skill challenge structure.
I view skill challenges to be a bit of a dice rolling crutch for DMs that want there to be rules about what works and what doesn't work in non-combat situations.