I haven't read all 13 pages to see if this has been mentioned, but this is my pet quibble that I'd love to see modded out. There is a really obscure rule in the game where the cost of moving across culture borders is increased to something like a full move or even the rest of your moves despite being on a road. I don't have the exact specific nailed down. I think it may only happen when you're moving into a tile owned by a civ you're at war with. Not if you're at peace. I don't think it happens if you're moving from an unowned tile into an owned one (but it might).
Anyways, I find it extremely obscure and illogical - it doesn't take any extra to move across roads within an enemy empire, so why would crossing the border be any different? If you're already at war, it's not like your artillery stops to have a chat with the immigration dudes... This comes up fairly rarely, but it always messes me up, because it's so unexpected - you run out of moves when you thought you had enough to attack / bombard / whatever. First time I really noticed it, there was a bridge at the border, and at the time I thought it was a special rule for bridges across cultures. But then later I noticed it again and no bridge was involved.
I've read though all the GlobalDefines and all sorts of tables, and haven't seen anything that would cause this behavior so I can nuke it... Please keep an eye out.