Thrilling, at first. Then I found out how "easy" it is to install the stuff. Something every administrator will love to do in order to support consolidation in his datacenter. Don’t you think?
Hypervisor technology and OS awareness of virtualization in general is definitively the way to go! But if you have to follow these four easy steps to run a Windows app on Linux on a Hypervisor:

Compile your Linux kernel with support for Xen [Linux specific distribution issues can be found here]
Create an .iso file [8 GB recommended size]
Create a new partition on a hard drive and copy the loopback file system to that partition.
Create the Xen config file point the domU at the new disk partition.

Come on, get serious. This is certainly not "…the beginning of a robust ecosystem evolving around the Xen technology." This is what Moshe Bar, Founder and Chief Technology Officer, XenSource may see and wants us to believe. There are way more serious projects revolving around Xen and virtualization. For me Windows-apps-on-Linux-via-Win4Lin-on-Xen looks more like trying to push a square peg through a round hole.

Nice try, for now I suggest we follow existing proven consolidation scenarios on our preferred OS platform, enabled by 64-bit support and wait a bit. And if you want to move from Windows to Linux, there must be an easier way. From **nix to Windows I know for sure there are many and easier ways with products like Virtual Server, SFU or the competitive products from VMWare and others.