Boons - how do they work?

I mean, everyone seems to know how they work and what they're worth... but I can't find a damn thing about them in any book (maybe I'm looking in the wrong places), so once I started having doubts about my understanding I have nothing to actually reference.

So how DO boons work?

This page does a good job of explaining different levels of boons and what they mean, though all discipline teaching is a Major Boon (unless it is higher)

It's a matter of "How much do I/they want them/me to do/prevent this?". It is perception based not a hard and fast system. Boons from some people are worth more (princes, elders etc) because of the level of things they don't consider an inconvenience for them. There is also the supply and demand thing, ask your self can someone else do it?.

Like a lot in vampire it's about societal pressure. If you or someone else refuses to repay a boon the social pressure can be put on so people will be reluctant to deal with you/do you favors/put their neck on the line for you even though your an ass-hat. Best be sure to pay those reasonable requests for boon repayment.

I think I'd be safe to say The generally accepted levels (and some of the most commonly seen uses) are:

Teaching a Merit - Minor
Teaching a Discipline (not restricted by someone that can crush you) - Major
Putting your self at risk to help someone - Major
Being injured helping someone - Blood
Getting someone out of torpor with blood - Blood

Both of these are pretty good guideline sets.