"How virtualization is actually implemented is generally split between x86 and UNIX servers." Reading this, you could almost think the author doesn't know the difference between a hardware platform and an operating system, no less thought about UNIX on x86. Which is especially funny, because one of the most interesting server virtualization technologies to come along of late is Solaris Zones.
My group put a fair bit of energy into evaluating paths to virtualization. VMware was out of our price range, and Xen we found to have a great core (the Xen kernel) but lacking in management tools. The story goes on, but we eventually settled on Solaris Zones, which entailed migrating our infrastructure piece-by-piece from Red Hat to Solaris.
If that sounds like a nightmare to you, consider this: The fact that Solaris is extremely robust well-documented, and behaves the way the docs say it does, has meant that migrating our Ruby-on-Rails apps, our MySQL databases, our NFS NAS servers, etc., has actually been a breeze from the get-go. This compared to the hair-raising weeks spent trying to make Xen's mess of Python scripts workable just so we should stick with Red Hat. On top of that, we get all the Solaris goodies like ZFS and DTrace, and even Linux virtualization for the apps that we might not feel like porting.
My point is, Solaris Zones is a burgeoning virtualization technology that should not be overlooked.