I have literally just downloaded the headphone calibration plugin. I only became aware of it on a MMWA-F (see what I did there?!) post the other day! Can't believe I spent out on the Audeze LCD-2's to find that even they need calibration!
It will be good though. I have been using an unscientific method myself of 'making an opposite eq to what I hear different in the car etc'. This just does it so much better and more accurate. I don't use my monitors now for mixing. As you can see from the webcam, I have some treatment in the studio, but I am no pro, so don't trust the room like I would my headphones. Also the room is 11'x9'x'8' so not too far off a perfect box - not good. The walls are deliberately tapered, but even still as I say, I am no pro!