I ran fissionessence's trap challenge last night. It went very well, considering it was the first one we ever did. They failed two of the first three rolls, then basically backed off and let the rogue (who couldn't fail his Acro rolls) do it. He got five successes in a row, the last one being aided by a player who made a successful Perception check.
Personally, I'd say that goes against the spirit of a skill challenge. All players are meant to participate, just like in combat. If a skill challenge caters too much to one class' skills (Rogue, perhaps, in this case), the challenge needs to be broadened to allow for participation from more players.
Subjective changes: I wouldn't have made proximity an issue for Arcana and would have raised the DC for Acrobatics. If the orb could attack at +11 vs Ref, why is a 13 Acrobatics a success? Also, I'd have opened up History and Religion as possible primary skills contributing to successes, with Perception and Insight as secondary or Aid Another checks (not leading to successes or failures but granting a bonus). Adding Endurance (being able to withstand the force of the orb or what-have-you) would also have allowed a Fighter to contribute, even if it only granted a bonus to another (he's taking the orb's force or attention, allowing another character to get closer or have a more unimpeded examination of the orb).
Not trying to be negative, just constructively critical. There's a lot more fun to be had when everyone has the opportunity to participate - that's what I've learned from running a few minor challenges.
I like how you had the successes count towards weakening the orb; it wasn't an all-or-nothing challenge. That makes the situation seem more realistic. The challenge also being a trap is a great addition. It shows a very clear penalty for failed rolls and makes the characters feel like they're competing against something, which can sometimes be a problem with skill challenges that don't have an NPC component.
My skill challenge: Blocking the Road.
Setup: The players were leading a group of refugees into the rocky foothills. A subset of the refugees were going to splinter off and take a path to a town no one has heard from in months, but the PCs wanted to check it out first. Not wanting to leave the main group on their own, in the middle of the night, three of the PCs decided to create an obstacle for the splinter group.
Level: 1
Complexity: 2 (6 successes before 3 failures)
(Participants: Ranger, Rogue, Warlord)
Primary Skills:
- Perception (DC 13): You spy a good bottleneck or chokepoint to create the roadblock. (can only be used once)
- Dungeoneering (DC 17): While not a 'dungeon,' this challenge involves the creative use of materials to create a roadblock good enough to delay the splinter group for a day or two. Only adds one initial success to the encounter; does not count as a success if Nature has been used successfully.
- Nature (DC 13): You are able to tell what portions of rock and weak trees can be used as roadblock material. Only adds one initial success to the encounter; can be used multiple times to give another character a bonus to Athletics.
- Athletics (DC 15): You're able to manoeuvre, lever or cut material from the area to create a block in the road.
- Endurance (DC 15): Used to aid another for Athletics; does not count towards a success or failure for the encounter.
Success: The group creates a roadblock that will hinder and stop the splinter group from arriving at the town for two days.
Failure: The group uses up materials in that area but does not create an obstacle. Anything barring the road can be moved aside with only a few short hours' work. Also, it is clear that terrain features were purposely cut and/or positioned.
It worked really well and was a nice follow-up to the roleplaying they'd done earlier to dissuade the splinter group of refugees from going to the town.