So I recently ran a skill challenge in my campaign. Cool story bro, but what did I learn? Well...
1) Post-errata DC:s are just crazy low. Of course I should have checked over the PC:s skills. Anyway, the usable skills need to be either limited (so everyone can't use their primary) or the DC:s might need a bump. I was using normal DC:s almost across the board, I could have thrown in more easy and hard ones. Which brings us to point 2...
2) Encouraging people to roll. One player eventually decided to pass. No skin off my back, but it's a pity that the skill challenge system as written punishes people for at least trying to roll with a sub-optimal skill. I'm thinking of throwing in a time-limit (long enough that the PC:s easily beat it if they all roll) and maybe abolish failures, like I've rambled about earlier.
3) The time limit would also limit the availability of trying secondary skills. I had a few of them in the skill challenge, which granted bonuses to some of the primary skills. (they didn't grant successes or failures.) Theoretically, the players could just have farmed them for all the bonuses before tackling the primaries. They didn't, because they're decent, but in theory it's something to watch for.
Oh, about those skill DC:s: Normal DC:s are the baseline, of course. Those skills are just kind of there. Where it gets interesting is the other two kinds. There is a school of thought that says finding easy DC:s should be a reward for "reading" the situation - Intimidate is usually hard, but it could be easy if you are in a position of power. I can dig that, but I prefer the following alternative:
Hard DC:s give you something if you succeed. Maybe it opens up an easy skill, or grants a +2 to some other skill (with a normal DC).
Easy DC:s need to be earned, either by reading the situation or by succeeding on a hard DC. Or maybe failing the easy DC has harsher consequences than usual - -2 to a few skills or something.
I don't really want to go with double failures for easy DC:s. The party is three failures from utter failure anyway, it seems harsh to make that two just because they tried a certain skill.
Stream of consciousness over, have a nice day.