December 3, 2010 update: The content on Technet has not yet been updated but I raised an urgent request today. I recognize that the content is still confusing but allow me to say that Group Chat with CU5 is supported with OCS 2007 R2 in a Windows 2008 R2 raised functional level and with Windows 2008 R2 Domain Controllers. I have confirmed the support statement with our Sustained Engineering team who owns supportability and fixes and I am also communicating this out to our support staff on internal distribution lists. If you have any further questions ask your account rep to call me direct, use the contact form or email toml (at) microsoft (dot) (com)
The release of Group Chat CU5 was eagerly anticipated by many, however our content was either confusing or inaccurate and we are working to fix that.
Here is what we know to be wrong, the change we are making and whether it is in process or under discussion.
1) Support of GC in Windows 2008 R2 Domain
2) Support of installing GC on Windows 2008 R2 OS (Member Server).