Caution for those who plan to move from Entourage to Outlook for mac:

I installed Outlook for Mac when it was released in order to benefit from the more stable (and backup-able) file structure. (Entourage's data file does not reliably backup with time machine).

Couldn't use Outlook until our Exchange server was updated, b/c it is not backwards compatible with Exchange pre-2007:
"Note: Exchange support in Outlook 2011 requires connectivity to Microsoft Exchange 2007 SP1 RU4 or later"
from http://support.microsoft.com/kb/2353366