Xen 4.0 beta is out
Some details here and here. This thread in the beta forums has some useful context as well.
The most interesting new feature is NFS shared storage system based on VHD files and Live Migration (XenMotion). There is also iSCSI based shared storage and support for 64bit Windows clients. In order to deliver a product now XenSource have delayed releasing 64bit support for Linux clients and their new admin interface is Net2.0 base, thus Windows only. Currently they suggest that Linux users look at the xe cli client which has been improved to deal with many of the new features. Their final goal is a web based management system, if they did something REST based in rails it would be great.
I don’t have time to do any testing right at the moment, but I’ll be putting it though its hoops some time in the next month. One of the things I’m interesting in finding more information on is the new xva format. So I can do some work on a deployment system.