a) Depends on the application. But money doesn't grow on trees.
b) Oracle: Replication, backup, support from application vendors, tools, tablespaces, looks great on resume.
PG: Ease of installation, ease of administration, porwerful feature set with small footprint, speed, psql; smart, committed team of core developers (in bright contrast to the MySQL team).
c) Oracle: Installation, administration, SQL*Plus sucks, huge footprint. PG: The oid problem with functions, VACUUM is pretty annoying (although this will be a lot better in 7.2), tablespaces; replication is here but not feature-complete yet.
d) Oracle: Very demanding system, for a very large installation. PostgreSQL: everything from very small to medium-large applications.
e) It is an issue, a very big one. You can't pretend it doesn't exist.
f) I haven't looked at Interbase or SAPdb, but they look like good options.
