These two posts prompted a few thoughts:
* I'm not sure which I dislike more - GMs who ignore backstory, or GMs who treat it antagonistically - but both are bad;
* As I've posted many times before, the original Oriental Adventures made a big impact on me, and part of that was that it brought familial connections and other sorts of bonds/loyalties (eg disciples to masters; monks to monasteries) to the forefront of the ingame situation;
* I think it's a real skill, as a GM - as in, one that can be worked on, reflected on, improved etc - to incorporate these background elements into play in such a way as to honour them, and treat them with appropriate respect and affection, while also using them to drive what is (typically, in RPGing) a dramatic or adventurous series of events.
The Burning Wheel Revised rulebook, in the section on Relationships (which is a formal element of PC build in BW) says (p 109):
If one of your relationships is your wife in the village, the GM is supposed to use this to create situations in play. If you're hunting a Vampyr, of course it's your wife who is his victim! Suddenly, you're swept up in a plot of terror or intrigue.
One thing that helps with this is if the system has the resolution mechanics to enable non-GM fiat resolution of the situation once the GM has set it up. But the GM's sense of when to push hard, and when to pull back a bit, remains crucial.