I can't speak from the dba perspective, but I mainly write applications
against Postgres and Oracle. I've used a dozen or more RDBMS's and
Postgres and Oracle are by far the most similar of any two.
When the two differ, its about an even split for when I say "I wish
Oracle did it like Postgres" and "I wish Postgres did it like Oracle."
Others have mentioned some areas where Postgres is lacking that will
soon be addressed such as CTE's. I'd really like to see Postgres
implement something like MERGE INTO, and stored procedures instead of
just functions.
On the other side of the coin, Oracle doesn't have a boolean type (in
SQL) which is annoying; you don't have to select from 'dual';
generate_series() is quite useful; and custom aggregates are easier in
postgres.