Looks like this thread is going pretty well but I'll add my experiences..

First the Code could be simplified a bit:

CREATE OR REPLACE TRIGGER TABLE_NAME_audit_info "
BEFORE INSERT OR UPDATE ON "'TABLE_NAME"
FOR EACH ROW
BEGIN
IF INSERTING THEN
:new.user_name := user;
:new.lastedit := sysdate;
ELSIF UPDATING THEN
:new.user_name := user;
:new.lastedit := sysdate;
END IF;
END;

For some reason howver I am not found of these triggers. They tend to add a lot of database IO.
It surprised me to find that the top two SQL statements on our databases where:
select sysdate from dual; and
select user from dual;

I couldn't figure out why because you would think the dual table when queried would not need any IO.
But from database statistic it seemed to do so. Oracle said it was because the query needs to create temp space.

Anyways I just added a preference to disable the triggers so that DBA didn't complain about the IO if they did a
TOP SQL query....

Anways the IO should be negligible in my opinion but I had to take the DBA's experiece into consideration that brought this to my attention.