Exchange 2007 Editions
It seems like the new Exchange 2007 Enterprise edition will now be only required for very large Exchange depoloyments, clustered or NAS based. The limits on the standard edition has been lifted and curiously enough it supports continuous replication, a former costly feature with 3rd party support only.
However, some of the Exchange 2007 feature such as unified messaging and forefront security will only be available with Exchange 2007 Enterprise.
For more information: