A couple of threads on G+ recently talking about using backgrounds skill checks, i'm not going to go on at length about them i just wanted to share my thoughts on some good use guidelines for people to mull over.
Players should be able to attempt to shoehorn almost any check into one of their backgrounds as long as it doesn't contradict existing 'game fiction'. It s up to the GM to decide whether you can use it, if i'm running a session the more creative and developed reason a players gives me the more inclined i will be to go run with it.
Likewise as a GM if your going to say no to a particular bonus you better had be as equally or more-so creative/developed in your reason why it cannot be used.
All of these things get easier with time as more and more game fictions is created, fleshed out and explored. And of course a player wont need to continually create new reasons for familiar situations, although I think it would be great to start reference past events for characters to achieve the same bonuses.
Another thing I like to do is to directly inform my players how hard a task is, I don't give them the DC but I'll inform them of of a rough difficulty range (Easy, Challenging, Hard, Impossible etc) Then I can change this between players based on the background bonus they give me, allowing more background checks to apply, but also making harder/easier based on its suitability.
How do you work your Background skill checks?