It appears that there are a couple of different ways that various
packages create users - postgresql futzes with useradd (which fails
a good portion of the time on reinstalls); popa3d (which seems to
work pretty reliably) uses sysutils/user (and seems to have worked
pretty well for me.)

Should this sort of thing be standardized? It looks like it was
discussed on 7 Dec 2000 (under the subject 'useradd is useless
for creating system users'), but most of the thread was devoted
to fixing useradd. (which, AFAICT, didn't seem to go much of 
anywhere.)