Hi Paul,
There's a simple answer to that, and a more complicated one. I'll try and give both.
If you want the closest possible print to your design then YES - keep your art in the largest colour space you can, and keep pantones and other spot colours as postscript. If you're sending the file to a printer that knows their onions, telling them your ideal is the way to go. Save as .pdf ensuring that you don't convert to a smaller colour space in the process and spot colours are maintained.
What this does is ensure that you're asking for your ideal - the printer should then push to the limits of the machines possibilities, giving you the closest possible matches.
Hudson's Edge - Colour Space | Hudson The gist of this is discussed here.
Here's the key thing to understand. CMYK or RGB numbers are device dependent. When you use a set of CMYK numbers representing a pantone, you're actually specifying how that pantone is best represented as "on a specific device". In the case of AdobeCS default - SWOP, ie. the best match an offset printer can achieve. That might be useful in some circumstances - but if your printer is a muppet, or if you don't embed the profile, those CMYK numbers could end up sent to another device and you'll get a different colour (discussed here
RGB or CMYK? Colour Spaces - what should you work in? | Hudson - the same CMYK numbers are SUPPOSED to give different colours on different devices - something many seem confused by.)
If your printer knows what he's doing, and you've saved your file embedding the ICC, he should print the colour you've asked for... and this is key.. you've asked for the SWOP CMYK equivalent of a Pantone - to reiterate - you've asked for the best match a SWOP certified offset press can get to your pantone. You haven't asked for the Pantone Colour! So, if you want Pantone Blue280, and my 10 yr old Mimaki JV3 can print that on some products, you'll get Blue280 if specified as a postscript Pantone, OR you'll get the dull SWOP CMYK equivalent if you specify the CMYK numbers. (OR if you use a printer who doesn't know what they're doing you'll get your CMYK numbers pumped straight to their device, and a random blue somewhere in the general vicinity)
I said the answer was complicated...
It gets more complicated when you consider that often a design is being printed on multiple media and you want the same colour across them all. Some medias might allow you to get to your colour, others might not take enough ink, or start out white enough, to get there. In those circumstances you don't want the best match on each media - you need to find the most limited, and have the other more capable products limited to match. (a fleet sails as fast as its slowest ship and all that.) I'd still advocate letting the printer do that work - but communication regarding the full scope of the job is essential to ensure a match across multiple media's. You could, in those circumstances, deliberately limit your colour, perform the conversion in CS, and send out the limited colour file for print.
I'm talking here from the point of view of a printer that completely understands colour profiles, colour spaces, and converting between them. If anyone in your production chain doesn't you have a couple of choices. 1) use people that know what they're doing with digital colour rather than those who've never taken the time to learn, 2) limit your colour to SWOP deliberately as a safe "anyone can print that" option.
Just to reiterate the key point here. If you send out CMYK numbers representing a Pantone the numbers are device dependent. AdobeCS and the Solid to Process PMS swatch book are both representing the SWOP Certified Offset Press. The numbers represent the best match that offset machine can achieve to that Pantone colour. They do not represent that pantone colour on any other machine.
So when you get a colour back that doesn't match the Pantone colour - don't be upset or surprised. You didn't ask for the pantone colour in the first place!
Finally to answer your two questions for my own company:
1) Yes please! Send me a file that describes what you actually want - Pantone postscript and embedded profiles. I'll give you the best version of that on any given media, or discuss the limitations of the different media if consistency across several is required.
2) I don't use Quark and haven't seen a Quark file in years. However, the info above will be valid for any program that uses Postscript labels and ICC profiles, and outputs to file types that retain that information.
Hope that's of use.
Regards,
Craig