As a follow up - how does one get colors in a 4-color sheet fed output to be more saturated and vibrant?
I'm just a photographer, not a pre-press person, but I do a lot of this work as part of my staff job. Even with a calibrated monitor and correct profiles, images do lose a lot on press. So I usually punch up the RGB file before the conversion -- add some saturation, and use a wide-radius Unsharp Mask to enhance local contrast. Then convert to the proper CMYK profile, do the final pre-press USM, and save it out as a TIFF.
Note that the RGB file looks "overdone" before the conversion. I realize that this seat of the pants method might not be "correct," but we get good results on press. It will probably take some experimentation using press proofs (printed) and several finished projects on the press.
Edit: I'll add that I start with a good 16-bit RGB file in ProPhoto or Adobe RGB.