I'm I the only one who find the RAW for skill challenge ok ?
I don't see a big problem.
EDIT : Well, I never used the side note about +5 on DC for skill checks.
For lvl 1 :
Let see : a moderate DC is 15
Character's best skill is on average +8 (trained +5, ability +3)
So he will need 7 on his dice (wich is 70% succes [getting a 7 on the dice IS a succes, only a result of 1 to 6 is a fail, wich is 30% odds], not bad at all), not to mention he could get a +2 to his dice if he provide an original/intelligent description of how his skill can be used in this challenge.
Keep in mind that players will try to use their best skills in each rolls. Just let them. You're doing a diplomatic skill challenge? How can the wizard provide help with his arcana skill ? Well, just let him tell you. If he comes up with a good or original explanation for it, let him do a check with a moderate dc (15) (maybe even granting him +2 bonus if his explanation is really creative/wise). Be open minded! Let say the fighter wants to use his athletic skill on the diplomatic skill challenge and he comes with an explanation like : "I dash as fast as I can to get to the city guards and tell them about the noble's treachery!" I would let him use his athletic skill with a DC 15 since this is an original idea of using his skill. But if, some levels latter, come by another diplomatic skill challenge and give me the same explanation, I would use a Hard DC and tell him the next time he should be more original (heck, if this new skill challenge is against the same noble, I would not allow him to do so and give him an in game reason like "this time, the noble expected you to do this and locked all the room's doors from the other side")
For a 4 succes before 2 fails, it works great. Each player will do one skill roll (and they WILL use his best skill to do so). Well, odds can come up with 2 fails or 4 succes before every character can make his roll, but in some case, some character can't find how to use his skill on this particular situation and he'll only be happy to find the skill challenge resolved before his turn comes up. For that matter, I don't use initiative. The first player to come with an idea how to use his skill on the challenge get to do his roll, then the next one, etc (but I don't allow a character do to 2 rolls before everyone could make one).
Then comes complexity 2, 3, 4, 5...
Now it messes the odds.
I changed the success/fail on those to keep an average of 70% succes (more or so) and on those I keep in mind that on complexity 2, I want players to do an average of 2 skill rolls each, complexity 3, 3 rolls, etc.
Here's my list :
Complexity 1 : 4/2
Complexity 2 : 7/4
Complexity 3 : 10/6
Complexity 4 : 13/8
Complexity 5 : 16/10
EDIT : Well, then again you could go RAW only removing the +5 DC on skill check side note and have a more or so ok skill challenge system without having to change things from the book.