Using different versions of Outlook for manager/delegate pairs (White paper)

http://www.microsoft.com/downloads/details.aspx?familyid=1A80D60D-566E-4985-BBA9-1AC6FEAF73C5&displaylang=en

When you use delegates in Outlook 2007, it is recommended that the manager and all the delegates use Outlook 2007 Service Pack 2

http://support.microsoft.com/kb/924470

Microsoft Forefront Server Protection Blog : Forefront Protection 2010 for Exchange Server RTM Capacity Planning Guidance

http://blogs.technet.com/fss/archive/2009/11/12/fpe-11-0-rtm-capacity-planning-guidance.aspx