Yes, I do use custom white balance. Most of my paying gigs don't allow for the use of RAW files for several reasons, most important being speed. If something in the scene is true white I WB off of that, otherwise I carry a small grey card. However, I don't run into the need for it often, as the presets are pretty close for the most part. And yes, I change the WB presets OFTEN, as well as ISO. Those are probably the two most used functions on my camera, next to the shutter button.