brundlefly
SONAR is smart enough not to apply dither except when the bit depth is being reduced.
 
Here's a post from Noel on the topic from some time back:
 
     http://forum.cakewalk.com/FindPost/1204822

All good - just read the link in your post brundlefly. Perfect - thanks for that. As I suspected dithering should be applied when bouncing tracks below 32bit and is ignored regardless of setting when not. Best left alone:)
 
And good news for Chris - unless you changed the render settings in preferences to something lower than the default 32bit you have not been dithering at all. Everyones a winner!

Thanks for all the responses and insight. I'm happy to hear that the dithering is only applied when it's necessary, even if dithering is selected.