So, I have this mechanic I usually bolt onto games that have a team setup with a leader character. The leader's player gets to tell everyone what to do and then roll a stat or skill to put some extra dice into the middle of the table. Anyone who is doing what they were told to do can use the extra dice and help guarantee their success.
Now I'm considering using a slightly modified version as a trust mechanic in my upcoming 4E game for Camp Nerdly. The gist of the scenario is that a double agent is leading the group behind enemy lines. Before each scenario, the NPC agent will be giving out real and "game world real" information about the enemies the group is about to encounter (e.g. "The wraiths are vulnerable to radiant energy" and "These wraiths are from the Sidhe Valain and can't suffer to be reminded of their noble heritage. You can distract them in battle with a few key phrases ...").
Whenever a player wants to get an advantage in battle, they can give me, the DM, a bead representing the trust they've put into the agent and steal a d6 from the middle of the table. They can add one to any roll they make.
At some critical moment, I'll take all the beads into account and roll to determine if the agent betrays them (the more they trust him, the more likely he will betray them). This will affect them for the rest of the game (a final, limited set of dice will make its way out onto the table if the agent didn't betray them, it will be empty if the agent does betray them) and make a turning point in the story.