The white balance tool lets you simply, pick on the image. But there is also the Auto function and the Auto mode (from the "Mode" drop down list). Each will yield very different results, in temp and tint (I am talking about RAW from a 5d2, with generic C1 ICC Profile and standard film curve, tethered studio portraits with and without strobes, just natural north light).
I am not satisfied with the different X-rite gray cards, they all give me too warm and reddish results. the "digital gray Kard" is not better, and Expo-disc is useless for this. Also, depending on where on the card you click, it gives radically different results. Question #1 is there serious comparison/tests available for gray cards.
The closest I can get (comparing a carefully calibrated screen and a print to reality) is by using the CROP tool to select the most of the gray card and than use the Auto "Mode". My second question is what do you do to get correct white balance with c1?