CM 2012 will be a whole new animal for many administrators that are comfortable with the architecture of the existing SCCM 2007. Site management and planning are different, secondary sites now require a database (SQL or SQL Server Express ), sites can no longer be re-homed into the hierarchy, a central administration site is completely new, and many site system roles have been replaced/added to meet the needs of this new product. The management console has been entirely re-engineered, and application and package deployment have also been changed.
All this means you had better start looking into the new requirements for future planning and possible migration to this product. There is no in-place upgrade available, but side-by-side migrations are possible. At this moment there doesn’t appear to be a way to have a SCCM 2007 site participate in a CM 2012 hierarchy like we did with SMS 2003/SCCM 2007.
I’ll be posting more in the future as we all prepare for the official release.