We've recently had a few users experience an issue with being able to see other user's free/busy calendar information. The interesting thing is, that this is only an issue if the user is choosing the attendees of a meeting request from their auto-complete list. Instead, if they choose the attendees from the address book, it works fine and they can easily see everyone's free/busy information.
Is this an issue with the auto-complete list? Or, some Exchange 2003/Outlook 2010 compatibility issue?