Yesterday I helped someone print a CMYK tiff to an Epson Stylus Pro 7000 printer under Linux.
That doesn't sound like a big deal, you say. Gimp-print has printed to Epson Stylus printers for a few years now, and who really cares about CMYK? Answer: the Stylus Pro printers are Epson's high end professional printers, and a lot of professionals like the extra control that CMYK gives them. Not to mention, Epson's own driver doesn't handle CMYK input.
We did this using CUPS. I had to fix a few bugs in CUPS; one of them may have been a bug in libtiff; the fix was a one liner, to enable CUPS to handle the CMYK TIFF. The other one was more substantive -- CUPS was converting the CMYK to RGB, only to convert it right back to CMYK. Note that CMYK is four channels, and RGB is only three. That meant that information was getting lost. In this case, what the file in question did was print 100% C, M, Y, and K. The conversion to RGB made it 0% R, G, and B; and the conversion back made it 100% K, and 0% C, M, and Y. Not an insignificant difference.
This is seriously cool to professional users. There used to be an affordable RIP (raster image processor) called Adobe PressReady, but it never supported the high end printers, and Adobe has since discontinued to it (speculation was that some of Adobe's partners, who sell much more expensive RIP's, didn't like the competition). Whatever the case may be, there's at least the germ of another way to do it. Ghostscript is, after all, a Postscript RIP (among many other things), and if it can do CMYK, it means that we, the free software community, can now start to compete in the graphic arts field.
That's not to say that we're anywhere near all the way there. Without color management, we still miss something critical -- the ability to map input colors to screen colors to output colors, and close the loop. So we're currently operating open loop. But we're making strides.