yes, I agree that database takes time from server. But I don't agree the same for timezones. In the below example from one of my servers, OS time zone seems to be GMT+12 and dbtimezone is +00:00 but still is showing the date /time correctly.

So, I am trying to understand the user of dbtimezone.

oracle@a1mumsum02$ date -u
Wed Nov 25 08:39:04 GMT 2009
oracle@a1mumsum02$ sqlplus '/as sysdba'

SQL*Plus: Release 10.2.0.3.0 - Production on Wed Nov 25 20:39:11 2009

Copyright (c) 1982, 2006, Oracle. All Rights Reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options

SQL> !date
Wed Nov 25 20:39:30 FJT 2009

SQL> select dbtimezone from dual;

DBTIME
------
+00:00

SQL> alter session set nls_date_format='DD-MON-YY HH24:MI:SS';

Session altered.

SQL> select sysdate from dual;

SYSDATE
------------------
25-NOV-09 20:39:50