A new KB article (2571388) was released yesterday regarding the logoff process on a Windows Server 2008 R2 machine running the RD Session Host role. The cause is a deadlock situation in the Csrss.exe process. To apply the hotfix you must be running Service Pack 1.
Article ID: 2571388 - Last Review: March 14, 2012 - Revision: 1.0
A Remote Desktop Services session stops responding during the logoff process in Windows Server 2008 R2.
"...Consider the following scenario. You install the Remote Desktop Session Host role service on a computer that is running Windows Server 2008 R2. You try to log off a Remote Desktop Services session on the computer. In this scenario, the Remote Desktop Services session stops responding. After some time, the computer stops accepting incoming Remote Desktop Protocol (RDP) or Independent Computing Architecture (ICA) connections.
You must turn off and then restart the computer to recover from this issue..."