I still see quite a few out there using both Imageprint and Colorburst for fine printing, to answer your first part... As far as superior results go, I'd say different methods give, well, different results, but would hesitate to say anything is superior. Even the best profiles vary from system to system... Bill Atkinson has (had? Lemmee see if I can find it again..) a page with "bouquets" of profiles he's built, the point being you can try and see which you prefer.
Yeah, here they are:http://homepage.mac.com/billatkinson/FileSharing2.html
The testing I've done with Colorburst, Imageprint, Xrite and Bill's profiles are all great, but it kind of comes down to, for me and most of the people who saw the prints anyway, a matter of taste. Kind of like film... which do you like better?
It's all really great, actually, we're no longer using this stuff to make an insufferable printer perform acceptably, it's more about tweaking and fine tuning.
Also, there's the question of black and white. Depending on which of several methods of printing you use and your convictions, some consider a RIP essential. (Joe Holmes just did some really interesting mega-pixel-peeping tests he sent me... crap, I don't have them here, not sure if they're public. I'll update if I can fine the email later.)
dammit, it wasn't Joe, it was Tyler Boley- his VERY interesting, if not over-the-top nerdy, analysis of B/W printing, with one RIP example, is here:http://www.custom-digital.com/
And FWIW, I'm pretty certain the actual "connection" with the output profiles is no different in CS4 than CS3... The interface is a little more refined, etc, but the math is the same. I'm sure I'll be corrected if I'm mistaken, though...
As far as any 16-bit issues, again, I'm on thin ice here, but I believe both Colorburst and Imageprint have supported 16-bit printing for quite some time now. (ducks, runs away...)