The wait is over and native support for Exchange 2010 RTM/SP1's archive mailbox inside Outlook 2007 is
here!
Hopefully, you'll soon be able to download the binaries for the December 2010 cumulative update from
this link.
Notable limitations about the Outlook update:
1. Working with Archive policies
2. Independent searches of the archive and the primary mailbox
The following Office editions are supported for archival support with this update:
Office Ultimate (retail), ProPlus (volume license), Office Enterprise (volume license), and Outlook Standalone (retail/volume license)
Thanks for the announcement,
Ankur Kothari!
Update: You can request the binaries from this link
here. It looks like the KB release notes have not hit the web caches yet but you'll be able to view the release notes for the Outlook portion
here.
Update 2 - 12/20/2010: Sounds like there are some known issues with this update so I would hold off using it for now. You can read more about the issues
here.