My preferred method of providing a safe .pst backup is to put the make the
user responsible.  Microsoft provides an Outlook backup utility that makes
this practical because it reminds the user every x days (where x is a user
setting) that they need to do a backup while exiting Outlook.

The utility is available at

http://office.microsoft.com/downloads/2002/pfbackup.aspx

Downside to this utility is that you need enough free space to make another
copy of the folders to be backed up, and the user is only reminded during
exit.  However, a user can do a backup while in Outlook with a toolbar pull
down (file/backup), so you can send periodic reminders to all the users.

In my opinion, that should be sufficient to meet any SLA.  My opinion is not
always in line with the reality of some IT managers that have already lost
this battle.

Bill Smoldt
STORServer, Inc.  SSSI