witter
"this update affects user mailbox permissions by revoking the 'Send As' permission in Exchange which has an impact on third party products such as BlackBerry Enterprise Server for Microsoft Exchange. Once applied, this update will prevent users on BlackBerry Enterprise Server from sending email from a BlackBerry or BlackBerry-enabled device, however users will still receive emails on their BlackBerry device. This is due to the BlackBerry service sending emails on behalf of a user when a message is sent via the BlackBerry device."
For a workaround, see: http://support.microsoft.com/kb/912918.
Thanks to Colin and Chris for letting us know.
witter