However I've moved on to using KVM for most everything. Having the ability to simply _have_ a hypervisor by default with no effort, no patching, no rebooting, no 'lifting' my system kernel out of Ring 0, etc etc is a wonderful thing.
And the other thing is that no special or weird configurations are needed. While Fedora with virt-manager provides a nice gui and other tools... for many of my tasks simply being able to launch qemu with screen and serial output to my terminal is quite convenient.
That being said, if people are using Xen and finding it useful and there are cases were it would be superior then it would be nice to get support into the kernel.