Quote Originally Posted by Isomenes View Post
But only if the character's Int is 14 or greater (or 16, if one goes with the more conservative modifier), which is not always feasible or even desirable. And it represents an opportunity cost. For a Human Fighter (the smallest pool with the greatest number of trained skills), an Int of 14 would net them an additional class skill. But what would he give up in exchange for training this skill?

Even so, there's more to skills than just using the ones you're trained in. Adopting this house rule imples a certain skill consciousness on the part of the DM, I suppose, in that you will want to test your players even in skills they don't have training in. But I can't see that it would undermine skill training entirely unless the DM were asleep at the wheel.
Note that my post quoted another post that referred to this plan:
Quote Originally Posted by Aahz View Post
One thing to note is that not all skills are mental: there's Athletics, Acrobats, Thievery, etc (just off the top of my head). Instead of awarding bonus skills for high Int, you could rule that if a player has a +3 or better bonus in a stat, she can choose to be trained in a single extra skill whose bonus comes from that stat (Athletics = Str, Acrobatics = Dex, etc.).

A high stat obviously already help any skill which uses that stat as a bonus, and it's likely that e.g. a high-Str character will already have a relevant skill like Athletics. But it would give nearly every character a single extra skill which will be relevant to the class.
Here, there is no opportunity cost. That is the problem. Allowing INT to give more skills just gives Wizards, Warlocks, and INT Warlords free power - if you're fine with giving an arbitrary boost to some classes and not others, then fine.