Digital BW, The Print

For the benefit of anyone else who may be facing the same decision,
here's how the current cost difference breaks down between the R1800 &
R2400:

Refurbished R2400 = $500
minus rebate      - $ 75
-------------------------
Total R2400       = $425


Refurbished R1800 = $350
minus rebate      - $ 75
plus MIS MK ink   + $ 30
plus QTR          + $ 50
------------------------
Total R1800       = $355

Cost of new ink cartridges for both printers seem to be equivalent
(though I'm not sure yet about ink usage).  For me this means I'll be
choosing almost entirely based upon subjective considerations.  

The R1800 (with the 100% carbon approach) offers the highest standard
in archival B&W on matte papers, as well as great color prints on
matte papers (with Paul's approach) and glossy papers (using Epson
inks).  The potential downsides are those that Clayton mentioned:
clogging, refilling and rechipping carts and an extra layer of
complexity (QTR).

The R2400 offers archival quality probably sufficient for most
people's needs (I realize that is highly subjective), a streamlined
and intuitive B&W workflow, excellent color and B&W results with both
glossy and matte papers (though you have to swap) with no additional
software, custom curves, tweaking, etc.  However, most people say that
color glossy results are better on the R1800.

Their dimensions and weight are almost exactly the same, and their are
custom paper profiles widely available for both.

Tough choice!