it's not that bad, as in Linux you have access to almost anything and can do many things sometimes easier than in Windows, I was going to write my own tutorial about monitor calibrating but here is good one which tells how it could be achieved:
http://www.linux.com/articles/113936Didn't read this article for ages so don't remember if in time it was written colorimeters was working under Linux, but from what I know now it's possible to use certain models, so you don't have to rely solely on your eyes for calibration.
