I had a phenominal experience with Obsidian on Saturday.
I'm the DM of an ongoing undead heavy game, since I started the campaign planning phases I've been envisioning a session where the PCs are called to some kind of summit, where the representatives of the various nations of the world debate what to do about the growing undead problem. However I was reluctant, because I knew that session would involve almost no combat and lots of skill challenges. After seeing the way my players approached the DMG skill challenge system (I use Diplomacy, throw dice, was that a success? No roleplay) I wasn't looking forward to running this session. For a while I considered scrapping that element of the game and changing my plans, but ultimately I ruled that out and started planning what I feared would be a boring session.
Then I found obsidian.
I gave my PCs a problem: Get the representatives to vote with them to declare war on the undead, I told them how many votes they'd need to have the war resolution pass, and told them who was leaning which way in a preliminary vote. I told them they had time to schedule four meetings with representatives before the council reconvened. It was amazing to watch my players digest the information I'd given them and formulate a plan. The back and forth, the questions they had for me, the internal party debates, absolutely great!
I'd designed a skill challenge for each of the representatives, when the PCs approached them we played through the obsidian skill challenge. It was great, it was roleplaying. It was basically a compound skill challenge, the vote on the war resolution was the larger, with each representative swayed to their cause a success towards the larger goal, with each representative played out in its own skill challenge.
As an added element I'd worked out ahead of time how each of the representatives felt about the others, if you tried to bring together people who dislike on another things were harder. As the PCs build their coallition who they'd already recruited weighed on the difficulty of swinging new people. When they approached a representative each of that representatives allies they already had in their camp reduced the DC by one, each of that representatives enemies increased the DC by 1. Knowlege of who liked who could be picked up in bits and pieces throughout the session.
The introduction of Obisidian, a few colorful characters, and a few props, made what I was worried would be the most boring session of my campaign into one of the most enjoyable for me at least.