Tidbits is reporting that the new License agreement with MacOSX Leopard SERVER allows for Virtualization of the MacOS.
From the Leopard Server License:
This License allows you to install and use one copy of the Mac OS X Server software (the "Mac OS X Server Software") on a single Apple-labeled computer. You may also install and use other copies of Mac OS X Server Software on the same Apple-labeled computer, provided that you acquire an individual and valid license from Apple for each of these other copies of Mac OS X Server Software.
While this change only applies to Leopard Server, the implications are that it will be easily possible for the 10.