Xen is already been available for a long while, now has VT hardware support so you get near native performance running windows as a VM, and is free for download.
Why would you pay $80 for crappy VM software that gets about 20% performance when you can download Xen for free?
I haven't used Parallels but people who have reviewed it running Windows on OS X seem to be fairly enthusiastic and it's only a version 1.0 product. Already there are some fairly substantial upgrades in the works. It's free to download and try so anyone could compare them for free.
Xen hasn't been around for a long time and it's support for Windows is very new and, as you note, only avalable on certain new Intel x86 chips. It may be a great technology when it matures but I suspect not for use by the faint of heart at the moment.
From the Xen Wiki:
"The paravirtualized approach we use to get such high performance has not been usable directly for Windows to date. However Xen 3.0 added Intel VT-x support to enable the running of unmodified guest operating systems, including Windows XP & 2003 Server, using hardware virtualization technology. We are working on implementing support for the equivalent AMD Pacifica technology."
Novell is at the front of the pack in supporting Xen into Linux. Red Hat won't support Xen until next year. This is all fairly new and is mostly targeted at enterprise servers rather than desktop users. See:
http
/www.novell.com/products/server/virtualization.html
And here's what eWeek reviewers had to say about XenEnterprise :
"Xen is a rather young technology, and anyone who's surveyed the current field of Xen implementations knows that besting them is leaping a fairly low hurdle."
(http

/www.eweek.com/article2/0,1895,2016548,00.asp)
For desktop users the most mature x86 technology is VMware Workstation. It costs $189, hardly cheap, but it's a product that was first released in 1999 and is now at version 5.5. See http

/www.vmware.com/products/ws/ (OS X version info here: http

/www.vmware.com/news/releases/mac.html).
Note that VMware's VMplayer software is free as are a lot of premade virtual machines using assorted Linux and BSD distros. If you search Google you'll find a number of sites with instructions on how to create a Windows virtual machine using VMplayer, obviously without all the bells and whistles of Workstation, but maybe with enough functionality for some users.
http
/johnbokma.com/mexit/2005/10/26/vmware-player-windows-xp.html
http

/www.ffnn.nl/pages/articles/linux/vmware-player-image-creation.php
Sure VMware has been around forever, so its stable, safe and well-integrated. However Xen blows it (and any other similar product) out of the water perfromance-wise. You need to consider if youre someone who needs a comfortable gui or someone who can get their 'hands dirty' with configuring a Xen-based system. I think if you're the latter, you wouldn't consider VMware unless you had a non-tehcnical or enterprise-level reason.
The eweek article you cited seems to be old and focused on Xen's enterprise product v3.0. It says it can't run windows. The current standard Xen download is currently at 3.0.2 and can run windows. The 'low hurdle' statement was in comparison to other enterprise-level products like vmware that costs about $500 per install because it comes with all the coprorate support etc. Basically VMware is a slow safe corporate product but for out-and-out techies its a pig in lipstick compared to Xen.
The audience of this board are mostly home enthusiasts and aren't probably gonna be paying $500 for any VM software for home use. The reality is that Xen works, is available for free download, and gives you about 5 times the performance of VMware if you have a VT-enabled CPU.