Microsoft recently updated their DirectAccess Unsupported Configurations documentation to reflect new guidance for DirectAccess deployments where the FRS is used for the distribution of Active Directory GPOs. DirectAccess is no longer supported in environments where FRS is used for SYSVOL replication.
What this means is that if you plan to deploy DirectAccess, domain controllers must be running Windows Server 2008 or later, and Distributed File System Replication (DFS-R) must be used for replication.
More details can be found here.