Here's some more information about what is coming down the pipeline with SBS Cougar. Seems like the Premium edition will allow the installation of 2 server to split applications like SQL and terminal services.
On that score David Mackie raises some interesting questions and issues with the Premium installation in his blog, especially given the new virtualization technology that will be available in Windows Server 2008.
I'm sure that we'll hear more about all this as the product near launch (June 2008 time frame) and I'm sure things will change and I wouldn't be surprised if some MAJOR things change! Time will tell.