I have builds of a new dom0 kernel (2.6.38-0.rc3.git0.1.xendom0.fc15) at http://koji.fedoraproject.org/koji/taskinfo?taskID=2755802 and xen (4.1.0-0.1.rc3.fc14) at http://koji.fedoraproject.org/koji/taskinfo?taskID=2753907
You may need one or both of the following hacks
Edit /etc/init.d/xenstored replacing the line XENSTORED_PID="/var/run/xenstore.pid" with XENSTORED_PID="/var/run/xenstored.pid" (I didn't notice they had changed the name of this file until after I tested the xen packages)
Edit /etc/sysconfig/modules/xen.modules to remove xen-netback from the list of modules in the for loop then add modprobe xen-netback netback_kthread=1 to the end of the file. The xen-netback module in xen/next-2.6.38 when I built the kernel still needed some work and setting this value makes it less likely to throw up backtraces if you try to use it.
Michael Young