Don't forget the "Secret Sauce"
Granted, booting off a Flash drive is no incredible feat. But don't forget that before Citrix forked over such a large chunk of change to fill it's server Virtualization gap with XenSource, it had filled in a WORKLOAD DELIVERY gap with the acquisition of Ardence a year prior.
With the Ardence product (now dubbed Provisioning Server) .. [Why not XenProvision ??] they have a game-changing solution. While Provisioning Server cannot yet stream the XenServer platform to Hosts, users can go absolutely DISKLESS by booting Xenserver from flash drives, and STREAMING guest instances over the network.
In most cases, they can use a SINGLE IMAGE of a guest OS to stream HUNDREDS of OS instances, and workloads from shared storage devices to server farms that have NO INTERNAL DISKS !!
Bad news for the likes of EMC (and granted, HP, IBM, HITACHI et. al.) when data centers don't need to store (and patch, and update) hundreds of one-to-one images.
Good news to the carbon-footprint-worrying crowd who can stop spinning (and cooling) a pair of mirrored 15K disks in every host in their racks.
Virtualization may be getting increasingly commoditized, but Citrix knows a thing or two about streaming stuff over networks, and regardless of whether Xen or Hyper-V end up as the chosen hypervisor, this is still a real solution to an enormous problem.