I find the auto-white balance excellent on my canon 30D and I almost always use flash or daylight as lighting so my camera stays set to auto white balance. I have played with the tungsten setting and it worked well.

Setting the white balance would come in most handy when the lighting is mixed (Example tungsten and daylight) and in that case I would set the WB to the more predominant light source.

Hope that helps a bit...

MaRKO