Here is another way to think about this,
If the typical photographic print needs about 400-500 distinct brightness levels to seem continous for a smooth black to white gradient, the 256 brightness levels of 8bit would seem as if not being enough.
Photoshop CS2 does have a dither option for color conversions to 8-bit color, so I would assume that if Photoshop is doing the color conversion for the printer, it would be dithering the 16-bit data of the RGB working colorspace into the 8-bit data of the paper colorspace.
If the dithering algorithm is good, and source material is at a high enough pixels per inch, then sending 16-bit to the printer should not be necessary.
> Do you see any particular posterization because of this?
Jani, I definatly do, even with a perceptually color calibrated monitor. Perhaps when Intel puts out a 10 Ghz chip, Adobe with think about dithering the 16bit data onto the 8bit screen for soft proofing...