The X-Rite ColorChecker does not make a big difference for the Leica M9, perhaps because the Leica M9 sensor already offers very natural colors.
This video goes over how to do it and shows a few examples on the effect using the X-Rite may have on the images.
And here is the link to the Lightroom preset for skin tones as mentioned in the video:
For more on the Leica M9 and Thorsten visit overgaard.dk/leica-M9-digital-rangefinder-camera.html
For more article about the X-Rite ColorChecker and WhiBal white balancing visit overgaard.dk/x-rite-colorchecker-passport.html
For X-Rite tutorials and to download the Colorchecker software and buy the X-Rite ColorChecker, visit xritephoto.com/ph_learning.aspx?action=videos