I am pretty sure the idea of skill challenges originated with an idea that an out of combat mini game could be fun (and why not!) and then an attempt was made to codify a certain amount of difficulty into a certain amount of xp reward. Which at its core is a pretty good idea. The issue however is that the implementation is just nearly impossible to nail in game, requires preparation, and at its worst it stifles player creativity.
I tried to use a version of the SC which amounts to players saying what they are doing and making skill checks. When roughly enough checks succeed to equal the difficulty that I am going for them you get the xp reward. But to be honest it is fairly arbitrary and not particularly engaging. Because at its heart it's about getting lucky with skill rolls to earn xp. Out of combat (or freeform as I described it above) is at its best when it is the players wits and imagination against the obstacle. And this is kinda the opposite of a skill challenge. I know you can bolt on auto successes etc, but in the end you just end up with a fairly unsatisfying experience in my opinion.
I ended up using the encounter building rules for an average skill challenge, at the players level generally, and awarded that amount of xp every half hour of solid roleplay/skill checks. Not scientific at all, but probably the most satisfying solution to me.