Back on Thursday, December 11, 2008 i published a blog that contained information on the fix for OAB Generation failing on CCR and SCC clusters. This went in to detail as to what the problem was for both cluster types. Tim McMichael who is our Exchange Cluster guru has written a very indepth detailed blog on how the Exchange Replication Service (Exchange 2007 SP1) and Windows 2008 Clusters works. If you have time please take a look at his blog: http://blogs.technet.com/timmcmic/archive/2008/12/23/exchange-replication-service-exchange-2007-sp1-and-windows-2008-clusters.aspx

Dave