Oracle-compatible outer joins will make porting modules over easier, for sure. The PG team's going to support SQL92 outer joins, too. It happens that Interbase uses the SQL92 syntax, so we'll probably end up rewriting Oracle outer joins to use standard syntax anyway if we end up deciding to support both databases.
The PG team and external contributors have added some nice Oracle-compatible stuff, i.e. to_char() most significantly.
