Lim,
It is no longer necessary to perform individual mailbox backups, and by default the view of them is not enabled. A new feature known as Granular Restore Technology (GRT) was introduced in 11d which allows you to restore individual items from a normal IS backup.
It is recommended that GRT backups be done to disk in order for the restores to be done quickly (you can backup to tape, but upon restore, the entire IS needs to be staged to disk in order to retrieve the individual item)
For more information:
Exchange Best Practices:
http://support.veritas.com/docs/285753
How to enable Legacy Mailbox backup support:
http://support.veritas.com/docs/285797