Have a look at the rules of the game in the new Planning for Large Mailboxes with Exchange 2007 white paper. This white paper covers the benefits of large mailboxes for both the end user and the administrator, the challenges that large mailboxes bring to an organizations infrastructure, and how Exchange 2007's features can help meet those challenges. Yes, >1GB mailboxes can be delivered to your users without breaking the bank.

More info: White Paper: Planning for Large Mailboxes with Exchange 2007

Source:→ Microsoft