I will agree with Hamlet and say that the Obligation system does seem a bit forced in this style of narrative game, HOWEVER, what it does do is get players to be good players and create interesting back-stories for the GM to work with and it gets the GM to be a good GM and utilize his players back-stories in his campaign.
I think the other thing the Obligation system does is present players with choices. Are they going to use the money they just got to pay down their debt or to pump some upgrades into that starship they are obsessing over? Will they attend that family wedding or go after the bounty that will gain them additional fame? (the wedding idea is brilliant by the way Northman, I will for sure utilize that in a campaign. Perhaps the wedding gets crashed by the boys in white and all hell breaks loose)
When they are in the middle of an adventure and suddenly faced with a legitimate decision (more than just, do we talk our way or fight our way out of this situation) that will have a large impact on the direction the story takes then suddenly the involvement level of the players has spiked. Now they are more invested in the story since they are having a direct influence on it.
However I think the single greatest thing about the system is the ebb and flow that will naturally come with it. Did your character just pay down some of that Favor obligation by diverting a shipment to his friend in need? Now perhaps he has gained some Debt Obligation owed to whoever the original recipient of the shipment was supposed to be.
I do agree that some of the Obligations are certainly harder than others to determine how one could pay them off, perhaps the final book could have this section enlarged slightly with a table of options on how to do that (similar to the one that gives some options for spending advantages).
It could include things like:
Addiction: Obligation is payed off when the player severs ties with his drinking or spice buddies. Obligation is payed off by eliminating members of the drug ring she was formerly involved with. Obligation is payed off by offering advice or financial aid to others struggling with addiction.
Betrayal: Obligation is payed off when the character eliminates people who participated in his betrayal. Obligation is payed off when the character puts trust in the people around him (sort of vague but this could be other party members looking after his equipment or something of that nature). Obligation is payed off when the character lets go of his betrayal and passes up opportunities for vengeance.
Obsession: Obligation is payed off when the player chooses an activity other than his obsession. (Conversely you could also focus Obsession in the opposite direction and the more you give in to your Obsession the less of a problem it becomes) Obligation is payed off after significant time is invested by the player in the object of his Obsession. Obligation is payed off when the character performs a service for the subject of his Obsession.
That is just a couple ideas for a few of the ones I have found harder to integrate into the game (2 of my players have Obsession and Addiction)