OK, guys here's the problem with the current 2010 upgrade strategy... you're killing IT admins everywhere.
2010 is supported on Windows Server 2008 and 2008 R2. 2007 is supported only on 2003 and 2008 (unless you're going to make an announcement on that with SP2, and let's face it, most of us are running 2003 still). Unfortunately, you've written in the past that doing a direct upgrade to 2010 from 2007 won't be an option.
This means, in order to upgrade, I have to acquire another server. Upgrade 2007 to SP2 upon availability. Install Windows Server 2008 R2, and install Exchange 2010 on the new server. Migrate mailboxes to it. This is expensive for small-to-medium businesses... servers aren't exactly cheap unless you really skimp on specs.
We can cut costs by deploying a "TEMP" server for the migration, but then we have to rebuild the 2007 server with WS2008R2 and E2010, and then migrate the mailboxes back to that box. This will take forever and a day for some folks... assuming, of course, that everything goes flawlessly.
Why not enable a direct upgrade path and WS2008R2 support for 2007 to make this easier? I've been using Exchange for years now at other jobs, and upgrading is ALWAYS the biggest hassle involved with the product. You absolutely MUST rethink this for future releases! This is 2009 going into 2010 as you well know, and having that kind of hassle, expense, and down time is inexcusable!