@J.Marley: Ya, if you want to add some new element to the world with your background, I think it would be fair game to use it. And I don't think you should just sort of dictate to the DM how you would like that to happen.
Hmm. I am not sure I was clear in what I meant in my initial post. Ought was probably a bad word to use.
When I write a character background, I do so as a guide to help me make decisions regarding how this particular character views the situations he encounters. For example, a character background of mine may look something like this:
Thoms, a young fighter from Furyondy. He is the youngest son of Hans, a simple farmer. An elder brother of his fought and died at Emridy Meadows, while another has made his fortune in the Wild Coast. With a twinkle in his eye and silver piece in his shoe, Thoms has arrived in Dyvers ready for adventure.
Thoms is young and naive, but capable with a sword.
From this, I can make decisions as to how Thoms would react to the situations that arise while playing the game. The background is a tool for me to use to help make those decisions.
Lately, the approach to character creation I have taken is emulating a particular personality. For example, my current character is based on various depictions of Falstaff. I don't really need to write much of a background as Shakespear did it for me.
Now, the above background is full of holes. There is no mention of a mother, possible sisters or brothers, other than the two listed. There is nothing about where in Furyondy he is from or how he got to Dyvers. Those issues are not
currently of interest to me - I may add them in at a later date.
What the OP asked was "[o]f course this varies according to players, but [what] is your view? How would you feel?," in regards to filling in holes in the background, to which my reply is I don't like it. It may not be an element that I am interested in pursuing as a part of play. Should it be something I am interested in, I'll make sure to mention it to the DM and give him permission to make use of it.
For example, if the party is heading to the Temple of Elemental Evil I may mention to the DM that Emridy Meadows is where an elder brother of mine died and he is free to use that information as he sees fit.
This is what I mean when I say player-initiated rather than DM-initiated.