For serious shoots (i.e. working with clients), I manually control the WB. However, since I shoot raw, I don't worry too much about it. Even when I manually set the WB in the field, I almost always adjust it in Lightroom to warm the images up, etc. Grey card WB is just a starting point for me. It's difficult to know how a client's skin tone is going to look in the LCD preview window so I typically fine tune it later in Lightroom.
BTW - I have found that Canon cameras do a exceptional job of dial in the correct WB automatically. I just tend to adjust it manually - more or less to keep things consistent - which makes processing the shots much easier later on.