Have you ever, at any point, run or played in a 4th Ed game?
I don't have 6 hours to waste on a single combat.
Have you ever, at any point, actually read through the 4th Ed rulebooks?
PHB, DMG, and MM when they first came out and used my own "greasy gamer fingers" to read them.
Borrow them when I want to remember something from them I don't have saved form the DDI articles. Why I asked for the page numbers cause I won't go looking for it.
Skill challenges get used when you're trying to do something that's more complicated than a single roll against one person's skill. Generally I would only use them if several players were doing different things with one end purpose in mind, and if there was some likelihood that failure would have consequences for the group. Without a specific situation in mind, it's hard to come up with concrete examples for a skill challenge.
If multiple people are all trying to got hold of information about a group and then come back and compare notes on what they've found out, that might be a skill challenge, if they're trying to do so without attracting attention. The more successes they have, the more information they get. Each failure increases the chance that they've attracted unpleasant attention, which might mean they get attacked or that the people they're investigating are waiting for them.
So you use them in response to a player attempted action or sequence, rather than a design for some non-combat encounter?
I could actually see THAT as a reason for skill challenges to offer direction to accomplish that. But not as a "design a non-combat encounter" approach.