Also for me with 12.04 64bit beta-2 with binary nvidia-current 295.33-0ubuntu1 on a Lenovo W520 with discrete graphics, with the nox2apic kernel option, VT-d can be enabled.
Linux xxx 3.2.0-21-generic #34-Ubuntu SMP Fri Mar 30 04:25:35 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
Also for me with 12.04 64bit beta-2 with binary nvidia-current 295.33-0ubuntu1 on a Lenovo W520 with discrete graphics, with the nox2apic kernel option, VT-d can be enabled.
Linux xxx 3.2.0-21-generic #34-Ubuntu SMP Fri Mar 30 04:25:35 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
Or else it is unstable / becomes unbootable.