MSDN now has a “SharePoint Server Migration Center” site: http://msdn.microsoft.com/office/server/moss/2007/migration/

SharePoint Portal Server 2003 and Content Management Server 2002 are truly integrated into a common architecture in Microsoft Office SharePoint Server 2007. Many tasks such as navigation, summary links, and scheduled deployments can now be performed by users or IT professionals.

SharePoint Server 2007 is built upon Microsoft Windows SharePoint Services (version 3), which is based upon Microsoft ASP.NET 2.0. As a result, you can also use functionality such as master pages, authentication providers, and navigation providers in SharePoint Server. 

You’ll not only find SharePoint specific upgrade & migration content, but you’ll also find MCMS related upgrade & migration content, including (all new content except for the second one, which was updated from it’s original NOV-2005 release):

• Mapping MCMS 2002 APIs to SharePoint Server 2007: Understand the changes, differences, and benefits of the MCMS APIs as implemented in SharePoint Server.  
• Planning MCMS 2002 Application Migration to SharePoint Server 2007: Use this guide in planning your migration to SharePoint 2007.
• SharePoint Server 2007 for MCMS 2002 Developers: See how SharePoint Server 2007 merges the functionality of MCMS 2002 and SharePoint Portal Server 2003 with new functionality to create one integrated set of technologies built on Windows SharePoint Services.  

The first and third links in the list above are great reads for MCMS developers who are looking at upgrading to WCM in MOSS 2007.

My webcast on The Evolution of WCM in the 2007 Version of Microsoft Office is also listed on the migration homepage… wooo!