I liked the [MENTION=42582]pemerton[/MENTION] post which stated you you just pick a background, and if the background is appropriate to the skill check, add the bonus. I like it because it allows that the capability of the character matches the expectation of the player without needing to go into minutae, and leaves both player and DM free to improvise.
FATE did something similar in the form of aspects, but you had many, and to invoke them you had to spend a fate point (the games limiting resource). It was actually really good.
This feeds into what I was getting at about PrimeTime Adventures; given loosely defined "backgrounds" players will, quite naturally, try to get the bonus from their chosen background to apply to as wide an array of things as possible. Broadly, this breaks down into two approaches to such bonuses that are not completely mutually exclusive, but are very different in focus:
1) Skills, backgrounds, etc. are limited by
scope. For this, each skill or background should have a clearly defined set of criteria by which it can be decided whether or not it applies to a given situation. These criteria are much better if carefully thought out beforehand, so this approach favours a limited list of skills that are
carefully designed in advance in an attempt to be clear, balanced and to avoid "subset skills", "obsoleted skills" and so on.
2) Bonuses from skills, backgrounds and other such "traits" are limited by the
number of times they may be applied - note that FATE does this by requiring a Fate Point expenditure. Now the traits do not need to be so rigorously defined; they can even be left for the players to write their own to best fit their character concept. The actual "rule" in use is based on the limited frequency of bonus use, so no "power creep" or "obsoleting" or such like is really possible - but some people object to this on the basis of "verisimilitude".
When I first saw this thread, my first thought was "Didn't Mike Mearls specifically say there would be a defined list of skills?" I looked for it but could not find it.
I found it.
https://twitter.com/mikemearls/status/208759333188665344
I believed you the first time
The context of the original discussion, though, was that [MENTION=19265]Connorsrpg[/MENTION] was saying that he and his group really liked the "unlimited skills" notion apparent in the playtest materials. I think such a system
can be done in a well conceived way, but to have
no limitation in the rules at all for either the scope or the quantity of skill bonus use I think will lead to a plethora of issues down the road.