I've referred to Portland as PDX since long before I found Flyertalk. Now I use the codes all the time both with my secretary (who books my travel) and my wife (emailing her when I arrive safely).

Only once did I have an issue, when my wife said "Where's CMH? I thought you were going to Columbus?"

I like learning new codes & figuring out how they came up with them. My regular airport used to be LMT (kLaMaTh falls)