Recommended Hotfixes for Hyper-V Failover Cluster based on Windows 2008 R2 SP1

Microsoft released KB2545685 with official “recommended” patches for Hyper-V Failover Clusters which are based on Windows 2008 R2 SP1:
KB2545685 – Recommended hotfixes and updates for Windows Server 2008 R2 SP1 Failover Clusters
http://support.microsoft.com/kb/2545685
How you can generally apply hotfixes or service packs in a failover cluster is also described in KB174799:
How to install service packs in a cluster
http://support.microsoft.com/kb/174799