Many people thought that Xen was dead and would have no chance against the “mighty” KVM solution, but well, the facts talk another language.
If you look a little bit closer you can see that
a) most clouds are powered by Xen
b) the new features of Xen really let the software gain an advantage.
The alternatives for hosting would be OpenVZ, Virtuozzo and maybe KVM, when it comes down to clouds only VMWare is a real opponent.
I definitely look forward to test Xen 4.0 and to use it for some special tasks!