For you people that want to run Office Communication Server 2007 R2 (OCS R2) on Windows Server 2008 R2, this have not been possible before and if you have tried you have gotten yourself in technical problems. But the wait is finally over; with a couple of fixes it is now possible. One sad thing is that there is no support for upgraded OS, you have to install new boxes with Windows Server 2008 R2 and then install OCS R2 on them and move everything from the old server to the new servers.
Read this article for instructions http://support.microsoft.com/kb/982021/
Worth mentioning is that group chat server is still not supported on Windows Server 2008 R2 and domain functional level cannot be 2008 R2 mode http://technet.microsoft.com/en-us/library/ee692314(office.13).aspx