PCalvin,
I've used Aperture since it was first released, and have printed photos on my Epson R1800 until a few weeks ago, when I added an Epson 3800.
I produced beautiful prints on the R1800, consistently, with very, very close matches to my calibrated monitor. To get these results, I always choose a profile for the paper I was using, generally Epson's profiles for its papers, and chose my printer, which was set up for the R1800 and the paper in use. ALWAYS printer color management was turned off ("No color management"). And, unlike another responder, I didn't get blocking in shadows. Rather, depending on how well I had processed the file in Aperture (for example, by using the Shadow slider in the Highlight/Shadow box), I was able to get, in the print, more or less detail, the "more or less" being entirely dependent on the extent of my intervention.
In short, I have been thoroughly satisfied with using the Epson R1800 and Aperture. For example, recently I had an image accepted for an international exhibition. The print I made for the exhibition was much larger than my R1800 could handle (20x30 inches), so a colleague - a VERY prominent and successful fine art photographer - allowed me to print the image on his Epson 9800. When I took my image to his studio to print, he looked at the file and urged me to rework it to remove noise and blocking that made the image really crappy. He showed me how the image could be cleaned up in Photoshop. I returned home and, with substantial work and experimenting, I was able to refine the image and produce a version that, when printed in his studio, he praised as "really fine." And, I did all of that work in Aperture, none of it in Photoshop. I even printed a segment of the image on my R1800 with the image sized at 20x30 so that I could see what the texture of the image in the print, on the chosen paper, would look like. (I used the same paper on my R1800 as I used on my colleague's 9800.)
So, it's my experience that gallery-quality printing on really fine papers (Epson Premium Luster; Hanemühle Photo Rag Pearl, used for my exhibition print) can be done on the Epson R1800 using Aperture.
Cheers,
Lou Outlaw