I just started to do some more illustrations and I'm facing this banding problem...
See this image: http://www.canstockphoto.com/social-network-members-with-text-clouds-7533900.html (You can magnify but don't see the banding because I removed)

When I simply turn the illustration into raster, due to the 256-step gradient approximation, there is a heavy banding in the background. (in fact there is everywhere but in the darkest shades it's more visible to the human eye). I was scared in the first moment, the artifact is almost unacceptable. To handle this problem I'm converting to raster the bkg separately, apply a slight amount of noise (to simulate dither), then put the other stuff over the bkg.
Illustrators, how do you make the jpg previews for your illustrations? If I export from AI or import the eps into PS, banding is unacceptable. Regardless of 8 or 16 bits.
Do agencies reject jpg previews because of banding? I didn't tried this, eg. DT also sells raster, so I didn't wanted to provide images with banding for those who buy jpg...

Today I got a reject from SF, "jpg preview it's not the same as in eps". The file in question was one of those with background banding removed. Probably this is the problem.