The problem with this method is that it removes all Exchange attributes, basically resetting them. The mailbox is in a disconnected state and until you re-attach the mailbox and re-apply Exchange attributes (email addresses just one example) you can potentially bounce mail.
Exchange 2010 SP1 has a new feature that isn't spoken of (infact TechNet documentation here still points to the above method!) This new command will automatically convert the mailbox to a linked mailbox without any disconnection or loss of Exchange attributes, and will automatically disable the account when applying the linked user.
Set-User -Identity Oliver@contoso.com -linkeddomaincontroller UserAccoundForestDC -LinkedCredential $(Get-Credential accountforestdomainadmin) -linkedmasteraccount Oliver@fabrikam.com
Try it, it works great!
Oliver Moazzezi MVP - Exchange Server