I run Skill Challenges in our 3.5e game quite often. I really like the idea of them. They're my favorite part of 4e. However, I run them almost completely like they were presented in the previews of 4e. That is, very narrativistic.
Last week, we had a skill challenge where a solar was guarding a gate that the PCs needed to get through. We simply kept roleplaying, me doing the solar's lines and actions, and the PCs doing theirs, as normal. Then one of the PCs made a great remark, something to the effect of holding up a trophy-head of a hezrou (she has the Trophy Collector feat from PHB II). I said roll Diplomacy, +4 for the head of the hezrou. She rolled, got over 20, and I said out of character, "All right, that's one success." Everybody knew then that we were on a skill challenge, and we always run them 4/2.
So then we just kept roleplaying. The ranger's sorcerer cohort sweet-talked the solar with some story using his Knowledge: Outer Planes skill instead of diplomacy, and someone else used intimidate or perform or some other skill, I don't remember but it wasn't diplomacy or any of the usual ones.
That's how we do it. Narrate what you're doing and how it relates to the situation, then roll the appropriate skill for the narration. It's been great. Like I said, it's probably my favorite new thing about 4e.