Some featured white papers on the Exchange TechNet site:
Technical White Papers for Exchange Server 2010
White Paper: Understanding the Relative Costs of Client Access Server Workloads in Exchange Server 2010
http://technet.microsoft.com/en-us/library/ff803560.aspx
White Papers: Exchange 2010 Tested Solutions
http://technet.microsoft.com/en-us/library/gg513520.aspx
Cheers,
Rhoderick
