PostgreSQL, MySQL and SQL Server have the function CONCAT_WS to concatenate strings with a separator. NULL strings are ignored. Admittedly, this is a function that is seldom needed, but in the rare cases were appropriate, this function can be very convienient. I suggest to introduce this function in Oracle, too.
Example:
SELECT CONCAT_WS(' ', title, first_name, last_name) AS name FROM persons;
NAME
---------------
Mrs. Jane Smith
Hank Miller
Mr. Jones