Some of my groups best moments have been with the skill challenges. It might be because they are a break from combat and gives plenty of opportunities for role playing....I haven't seen a single skill challenge I liked...
I haven't changed the skill challenges, but I haven't been very strict with the rules. If you can talk me into allowing a skill, you can use it. For instance after failing to help the dwarves with some mechanical stuff they wanted the characters off the whole thing before it got totally messed up, but one of the players used diplomacy (and some good role playing) to be allowed some more time.
I was quite sceptical to the skill challenges before I ran them, but if you run them a bit loose they work really well.