One reader points out that one significant new feature in Intel's upcoming Yonah Processor is "Virtualization Technology". Intel describes it as "allowing a platform to run multiple operating systems and applications in independent partitions."
The examples of use Intel provides include uses for administrators performing background system upgrades as well as separating business and personal use environments. The most interesting potential use is described here:
Home users could create virtual partitions isolating multiple user environments such as dedicating resources to a PC game, productivity, and personal video recorder-type environments
Potential uses under Apple's implementation of the Intel processors, of course, include the possibility of launching multiple operating systems, such as Windows and Linux, alongside Mac OS X. Alternatively, Tiger's Fast User Switching could be expanded to provide completely independent environments.
This Intel presentation slide posted on Anandtech's article from Intel Developer Forum 2005 confirms that Yonah is expected to include Virtualization Technology.
This technology brings back up a tamper-resistant code patent which Apple was recently granted. The patent description curiously also had a description of the use of multiple operating systems:
Apple also talks about securing the code while interchanging information among multiple operating systems. Linux, Mac OS X and Windows are called out specifically in the filing.