Ok, have figured this out...
1) When trying to install anything using apt-get, I would get the following error:
Setting up spamassassin (3.3.2-5+deb7u1) ...
dpkg: error processing spamassassin (--configure):
subprocess installed post-installation script returned error exit status 1
Setting up libdpkg-perl (1.16.14) ...
Errors were encountered while processing:
spamassassin
E: Sub-process /usr/bin/dpkg returned an error code (1)
2) I had to dig into the /var/lib/dpkg/info/spamassassin.postinst file, to find this command generates the error:
su debian-spamd -c "sa-update --gpghomedir /var/lib/spamassassin/sa-update-keys ...
3) The debian-spamd user already existed, but I had the login shell set to /bin/false, so the su just returned exitcode 1
4) Once I changed the shell to /bin/sh, apt-get install worked
5) I did get this warning:
Setting up spamassassin (3.3.2-5+deb7u1) ...
gpg: WARNING: unsafe permissions on homedir `/var/lib/spamassassin/sa-update-keys'
Starting SpamAssassin Mail Filter Daemon: spamd.
6) But I ran the following, and cleared that up:
chmod -R 700 /etc/spamassassin
chmod -R 700 /var/lib/spamassassin
Thx!