Xen 4.0.1 Released
RELEASE-4.0.1 has been tagged in http://xenbits.xen.org/xen-4.0-testing.hg
Browsing the above URL will show the mercurial changelog contains many many bug fixes since 4.0.0. We recommend all users to upgrade.
A source tarball will soon be available from http://www.xen.org/products/xen_source.html