My main desktop computer is a linux box with three screens. Today I calibrated all three screens, one of them for the first time ever.
An aside. There are two real ways to calibrate a monitor. The cheap option is to use a colourimeter: a device which measures red, green and blue levels. Software reads the measurements via USB and constructs an colour profile for the monitor, and the video driver uses the profile. The better way is to use a colourspectrometer, which is the same thing, except that it measures many, many wavelengths instead of just R+G+B, so the software can produce a more accurate profile.
I have a colourimeter called Colorhug. It's cheap, has good linux support and I thought it was fast: Perfect for people who use linux for work, don't really need colour, but do need a pleasant working environment. It actually isn't all that fast yet, although that is improving.
The software is supposed to work with the KDE (at least on Ubuntu, via Pascal de Bruijn's PPA), but I had endless problems with that, so I used unetbootin to make a USB stick from the Colorhug Live CD, booted it, calibrated all three screens, and copied the three *.icc files to the stick. Back in Ubuntu I applied the *.icc files in the KDE.
dispwin -d 1 /home/arnt/icc/2100-left.icc applies 2100-left.icc to my left screen (an Eizo S2100, hence the name).
Now I have pleasant, matching colour across all screens. Why should a programmer such as I care about that? Well, the letters in my emacs window are somehow better to the eyes. The colour may not be good enough for photographers, but I am not a photographer, I just work with computers and appreciate having good working conditions.
The whole procedure was amazingly simple. There were only two problems, and they weren't software-related at all. First, the Colorhug has to be stable against the screen. I tilted the screen, draped the Colorhug by its USB cable against the top of the monitor frame, wriggled the cable until the device laid stably against the screen, and then I taped the cable to the monitor frame. Second, I forgot to reset the colour adjustment on all the screens before calibrating them. Chores defeat me.