I strongly agree with this.On the subject of Skill Challenges, I think the big problem is that they didn't give any sound advice on how to actually implement them.
I'm less sure about this. I generally do let my players know they're in a skill challenge, especially if its of high complexity, because otherwise they don't have all the information they need to make sensible choices about how to use their resources (like powers, items etc).Never tell your players they're taking part in a skill challenge until you give them the XP for it.
I see it as being a bit like combat: I don't generally tell the players what the monster hit points are (unless I want to taunt them about leaving a monster on 1 hp!), but will tell them if a monster is bloodied; and most of the time they know how many monsters are on the battlefield (although occasional exceptions to that, like invisible lurkers etc, can be fun).
Likewise in a skill challenge - I try to give enough information to let them make sensible mechanical choices, while not necessarily giving away everything that turns the situation into something purely statistical rather than having some elements unknown to the players because uncertain to the PCs in the fiction.
Does that make sense?