What roles/features require 2008 Forest Functional Level?
… and/or domain functional level? There is a table on the following TechNet page that outlines this info. It has been a re-occuring question in my recent trips! Note that the domain functional level is the important factor for 2008, as that enables new features including fine grained password policy.
http://technet2.microsoft.com/windowsserver2008/en/library/34678199-98f1-465f-9156-c600f723b31f1033.mspx?mfr=true
