When our organization was on ex03, as an Exchange Admin, you could access anyone's mailbox within OWA by simply appending their mailbox alias to the end of the OWA url. With ex07, within OWA, if you select 'Open Other Mailbox', you'll get a permission error. You can explicitly add yourself 'fullaccess' permissions to the mailbox and wait for AD to replicate, but I don't understand why group-inherited full access isn't sufficient.If this has already been covered, I apologize.

Its the same in both version of Exchange. You have to give the account permission either on each mailbox or on the database object. http://support.microsoft.com/kb/556045