I just did the upgrade of my linode (which hosts mhvlug.org, planet opensim, dague.org, and a few other sites) to Xen. I had put in the request to join the beta for Xen a couple weeks ago, got in, and was slow on my side to actually kick off the migration (which was painless, but required about an hour of down time). It turns out that all of linode is now going to Xen. Based on very simple latecy tests, the box feels much snappier on serving up wiki pages.