not really canon or even video specific - but why don't cameras give you the ability to lock WB the same way you can lock exposure and focus? ie - use the auto functionality to get the pic and then lock it down with a single button press.

They do. With the XL-H1 put the WB dial on one of the preset numbers, aim the camera at a neutral card or put on an Expodisk and aim at the light source, press the balance button and when the white ballance annunciator stops flashing you have locked in a white balance.

If you want to lock in a white balance determined by the auto balance mechanism while looking at a scene rather than a gray card just to the same thing i.e. turn the WB knob to one of the preset positions and press the button. The white balance setting will be recorded and the camera will use it until the WB knob is turned to the other preset, back to auto or to the K position.

While that works it would be a nice feature to put the white balance in auto mode and then simply press a button to hold it there until you want it to go to auto again. Exactly like exposure lock works.

the method described by AJ is not reliable, particularly in changing conditions. Furthermore you cannot use it while shooting - in the sense that switching from A to preset will create a noticeable shift in temp.

They provide an exposure lock button even though switching to manual does the same thing...