This script lets you monitor the SQL Area. The username shows which Oracle user first submitted this statement for parsing; the first_load_time is when the statement was submitted for parsing.
select sql_text, executions, disk_reads, buffer_gets, d.username, first_load_time from v$sqlarea v, dba_users d where d.user_id = v.parsing_user_id order by disk_reads desc ;
Use this script to give you information on currently running SQL and on who's running it.
select * from v$sqlarea sq , v$session s where sq.HASH_VALUE=s.sql_hash_value and sq.address=s.sql_address and s.status='ACTIVE';