I've had to learn to be able to think in pounds since I've been coming here, now conversion arn't difficult...though when somebody still says "4 sticks of butter" I still occasionally do a double take (that would be the equivalent to 1kg of butter here).
When I'm in a metric country, I don't even try to convert. I go to the store and find something similar in size or weight, eyeball it, and just learn how much I want that way. I'm not a mathmetician. I forget it as soon as I'm home, but when I'm away that works. For recipes, you do have to convert, and I do own a few cookbooks written in metric. Most measuring cups have both, so no problem.