I've seen the crash too (Core2Duo T6600) and the only way to work around it for me was to completely remove all of Ubuntu's Xen stuff and install the latext Xen 3.0.4 from source. Before, it would freeze when starting the 3rd guest, now I can run as much as I like.
-- Dom0 crashes upon start of second DomU https://launchpad.net/bugs/71348 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
