I got Outlook Anywhere working fine on Windows Server 2008 without any special modifications. This server is CAS, HUB & MBX, as well as Active Directory Domain Controller (+Global Catalog). Initially Outlook kept prompting (endlessly) for credentials when using NTLM authentication. (got countless complaints about this from my users) However, it seems to have been fixed now. Not sure what did the trick.
I still have endless prompting on the /OAB virtual directory though. Trying to navigate to /OAB/[guid]/oab.xml works initially, but after some time (settings being applied periodically by some Exchange service?) it fails (HTTP 401).
IIS7 Failed Request Tracing is not helping, NTFS permissions seem correct. After making some modification to IIS7, it seems to work fine again, for a few moments.
To bypass this issue, I've resorted to using Public Folders to distribute the OAB. I'd still like to be able to fix the /OAB issue though.