As I mentioned before, we should probably see a few updates to Exchange 2007 and a sooner-than-expected SP1 due to the incomplete and buggy RTM version.
This is the first one, an update to Windows Server 2003 x64 to support large memory with Exchange 2007. How large is large? The KB is not published yet, but I bet that more than 3GB more is pretty large.
It appears that Microsoft is still vague about how large is large but the article says up to 2TB. Time to fetch more memory for my server. oooooh 2Terabytes. I could live with that.
KB:
http://support.microsoft.com/kb/918844
Download the patch here: