I printed the "InkDensity.tif" pattern with three different paper settings (Premium Photo Paper Glossy,Ultra Premium Photo Paper Luster, and Premium Photo Paper Semi-Gloss) and they all printed exactly the same.  I've checked "ICM" and "Off" in the printer driver, and turned color management off in Qimage (no profile selected).  I tried reinstalling the R1800 printer driver, but that made no difference; all three gradients looked axactly the same.  I'm stumped.

Thanks Mike.  I'll give it a try.  I'm somewhat limited in my paper type choices because I want to print in "Photo RPM" resolution.  I've chosen Premium Photo Paper Glossy, but my other choices for Photo RPM are:

Ultra Premium Photo Paper Luster
Premium Photo Paper Semi-Gloss
Velvet Fine Art Paper
Ultra Smooth Fine Art Paper

Any suggestions on which might work best?

I'm using an Epson Perfection 1250 scanner, Epson R1800 printer with Injetfly inks printed on HP Glossy Roll paper (leftovers from a large-format HP printer).  With other papers I have been able to get the usable range to 0-255 for all three colors (RGB).  With the settings I use, the scanner is able to detect differences between 21, 22, and "23" on the IT-8 grayscale, and the profiler tells me I have "excellent shadow detail".  It also tells me that I have only 3 boxes at Max/Min on the printer target.  Could it be, as Steve W suggested, that there is too much ink?  Would using the "bright" target improve things?  I normally use gloss optimizer on my prints, so I printed the target with it; would it help to profile without the optimizer?

The profile actually prints quite nicely with a little tweaking in the editor, and with additional grayscale tweaks with AMS Color Darkroom, I can get a blackpoint of around 15 and a whitepoint of about 250.   

After creating a printer profile, PP supplies several parameters about the profile:

Exposure: 241.
Note: 2 patches marked with "X" are at minimum/maximum brightness. 
----------
Printer/paper/ink dynamic range: 76.9
Printer/paper/ink coverage of Lab space: 11.6%
Smoothing required: 2 passes
Printer profile usable range: 0-255, 26-255, 0-255

Which of these is most important to optimize?  For instance, another profile gave the following:

Exposure: 241.
Note: 3 patches marked with "X" are at minimum/maximum brightness. 
----------
Printer/paper/ink dynamic range: 88.9
Printer/paper/ink coverage of Lab space: 15.9%
Smoothing required: 2 passes
Printer profile usable range: 51-255, 64-255, 51-255

The dynamic range and coverage of Lab space are higher in the second one, but the usable range is smaller.  So which parameter(s) would one rely on in judging the quality of the profile?

As a side question, what does it mean in the second one that the lower limit of the usable range is only a minimum of 51?  Is it that the original scan is lacking shadow detail?  Can I improve on it by tweaking the scanner settings to bring out more shadow detail?

How do I turn off "Automatic Login"?

Take a look at AMS Color Darkroom.

http://www.antelligent.com/pages/ps_plugins.html