Be aware the CompletePC Backup functionality doesn't backup your ost files. This is not a big issue because this file can be regenerated by the Exchange server the next time you connect.
I found the explanation why Vista doesn't backup this kind of files on this blogpost.
Basically because this file changes a lot it could take quite some IO to keep a shadow copy of this file.
<p>Dynamic files such as the system swapfile and the OST don't belong on a backup. It's a good thing VISTA recognizes this.</p>