For critical shots, I do a custom white balance, particularly, if there are no good white/black/neutral grey points to do a soft white balance in photo editing software. The RAW adjustments are all good and well for mood shots, but for color accurate reproduction it is better to make adjustments before shooting, and not adjust the RAW files further. Sometimes there is no option for including a color checker (e.g., compound microscope images).
On my 5D2 I tried a few times specifying K values based on Minolta Color Meter III readings from flash. However, the AWB turned out better, so I did not try it further. Those were some macro shots, so not sure whether this has an effect.
Being Kelvin aware is a very good thing, particularly if you have multiple light sources with different K values. The eye/brain is extremely efficient in adjusting for it, but the camera is brutally straight faced about it. I notice it a lot when I tried to mix an Einstein 640 with a Speedlight 580. The Lee filter sample booklets are great to make all sorts of LB filters for the 580. Then it is also good to know the mired system, and how to chose the right filter.