I've gotten a real kick out of using the Education skill to represent literacy vs. illiteracy. I often use handouts in my game and its a blast to give a character who can't read a handout with a bunch of gobbly **** on it, only to have that character find someone who can read it.
I run multiple games and in all cases, the majority of the party members are illiterate. This adds a nice element as the players try to work around it. I even have some players looking to take Education as a non-career advance, just to be able to read.
Similarly, I've used the economic tiers the same way. For example, if I have a player in the brass tier speaking with someone in the gold tier, I'll throw a misfortune their way during social encounters, and vice versa. I've had a few players spend money of different clothes so this wouldn't occur.
Any other ideas?