@scrape thanks!
@WGR
no, probably I can't explain myself. However, it's just like that to me bonds are the actual fuel of character motivation. When you look at the sheet, you see that most informations about the character's history and personality comes from the bonds, and so his goals. And you want one bond resolved and explored by the end of the session, so what better way to do it than menace it with an Impending Doom? Now I realize what does it mean that bonds are alike to burning wheel's beliefs.
The game I'm currently running, the wizard known incriminating secrets about the thief, that is the thief betrayed his brother to save himself from jailtime. My impending doom is: his brother (along with other important npcs) is going to be zombiefied while in jail. And the wizard foresaw that his marriage with the ranger will save the elven kingdom, and here you are another Impending Doom. But even small things, like the druid that owes her life to the fighter but at the same time believes he smells more like prey than hunter, evolved in "they were hunting pirates together, and the last battle was very chaotic, with the two of them going like gimli and legolas counting orcs" -> juice for a danger full of pirates and an Impending Doom that will fuel their bond!
Probably this is something more adeguate to my gaming group. If I do fronts not strictly related to their bonds, the players enter in a "videogame-y quest-y mode" where they forget about their bonds and just try to prevent the impending doom. As for myself, as the GM, I need an explicit flag to build coherent fronts that are not just "quests" but involve the characters on a personal level, and I found it in the bonds.