I'm a "fine art" photographer, sell my prints in a few galleries, exhibit in museums, etc. I have been using the z3100 for month and a half. Almost all my work is in color. With the current firmware and without a rip, I have been printing images that match and often exceed what I was doing on the Epson 9800 (both without a rip). Just installed the APS which gives me more color targets to profile my paper with. Very slight shadow improvements so far and slight improvement in some colors. Still not sure if it was worth the extra $700, need more testing on different images.
All that said, my best prints were with a Ergosoft rip on the Epson 9800. I haven't been able to improve on those images with the z3100 (no rip). A rip helps smooth out dark shadows by making things appear to have same density across the image (very little gloss differential), among other things. I still think the z3100 would get better with a rip, but I think none are available yet. (mac or pc) Colorbyte is coming out with one any day now for the mac (I'm on a mac).
Bottom line, get some prints done and check them out. The biggest plus, I imagine, with the rip will be ability to set up multiple images on a page with different or same sizes. Maximizing your sheet, etc. Everything else will probably add that extra "2%" improvement that only very discerning photographers will notice on very picky images. For Black and white, there may be improvements as well but my limited testing using the printer to determine colors (instead of Photoshop which is normal), has produced great quadtone images on rag paper (again, no rip).
I may buy a rip in the future if I can justify the $2000-$3000.
By the way, all the discussion about image quality and the z3100 has been around that last "2%" improvement to get to the ideal printer. Most were concerned with matching artwork that is being reproduced, not printing photographs. Alot of improvements have been made by HP in a short time around paper issues, red issues, etc. with firmware (and soon driver) upgrades. I'm confident they will keep moving/improving.
Good luck,
Doug