It's still not fixed for me with Ubuntu 10.10 and VirtualBox 4.0.4, further information and logs on the upstream bugtracker (which I also reopened).
** Changed in: virtualbox-ose (Ubuntu) Status: Fix Released => New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/455112 Title: VirtualBox performance is much worse when Intel VT-x is enabled -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs