We find much better results designing in RGB.. ESPECIALLY with Corel. CMYK exports from Corel give very muted, washed out prints.
I design all raster elements in RGB.
However, I use a CMYK swatch table for vector elements in my designs. It's just easier for me to tweak colors that way. If I'm trying to match a Pantone color, for instance, it's easier for me to work in CMYK where I can add a little yellow and subtract a few percent magenta. I don't have a good enough understanding of RGB to make those kind of adjustments. And in these instances, the on-screen representation of the colors is not as important as the final output.
So, often I'll have RGB bitmaps used in conjunction with CMYK vector elements and gradients.
Design in CMYK, export as RGB. 99 out of 100 come out very close to what was on the screen. Of course we have Pantone charts printed with our favorite settings and use those to color match/color choose when necessary.
After talking to one of the RIP companies, as I understand it, the RIP has to convert CMYK images to RGB in the RIP process before it prints anyhow. Even though the printer may print CMYK, the RIP doesn't necessarily work that way. I was told to design in RGB for anything that has to go through the RIP software. If you are designing something that isn't going to be RIP'd (i.e. business cards or brochures) you may be better off designing in CMYK.