Our company is currently doing the following (very successfully):
 
1)  Our mission critical application (encompassing order entry through to
general       ledger including manufacturing operations) is running on an
HP3000 Micro/XE      while I am setting up our new 918LX.
2)  We have 5 or 6 (I can't remember which) HP-UX workstations running a
HP's        cad program ME-10.  One of these is acting as a file server
for all of our               workstations, PC's and Macs.
 
The HP3000 machine seems better at handling high volume transaction
processing.  It is also extremely reliable.  This is why we choose it to
run our main application.
 
The unix boxes are much better with graphics (cad) and seem to do very
well with serving our network.
 
E-mail me if you want more specifics or to talk with our Engineer who has
set up this entire network.
 
Good Luck!