Check out these videos showing Xen virtualization VGA passthrough: 3D gaming benchmark.

Specs:

Host Operating System Domain 0: Fedora 11 Linux x86-64 64-bit
Domain U: Windows XP Home Edition SP3 32-bit HVM Virtual Machine
Xen Hypervisor Version: 3.5-unstable changeset 20143
Paravirt-Operations Dom0 Kernel: 2.6.31.4 (Jeremy Fitzhardinge's git tree)
Intel GFX Passthrough Patches Applied: Version 1 (Provided by Han Weidong Intel)

Motherboard: Intel DQ45CB
BIOS Version: 0093
Processor: Intel Pentium Dual Core E6300
Graphics Card: nVidia GeForce 8400 GS PCI Express x16
Memory: 8GB DDR2-800

Thanks to Mr. Teo En Ming.