Running latest ESXi 4.1 with two Windows 7 64-bit clients:

Setup:

• MB: ASRock X58 Extreme
• CPU: Intel Core i7 920 @ 3,8GHz
• RAM 12GB (3x Kingston 1600MHz non ECC 4GB)
• ESXi drive: 8GB USB stick
• NIC: Realtek RTL8111DL (onboard with custom drivers)
• First client Windows drive: OCZ Vertex 30GB @ ICH10R
• Second client Windows drive: WD Raptor 74GB @ ICH10R
• Graphic adapter: Sapphire (ATI) Radeon HD 4850 X2 2GB (dual GPU card with onboard PCIe bridge chip) (passthrough)
• Graphic adapter: Gigabyte (ATI) Radeon HD 2600 XT 256MB (passthrough)
• Audio adapter: Bgears b-Enspirer (PCI) (passthrough)
• USB: Two ports passed on to each Windows installation

• Running one GPU maximum RAM for Windows to run is 2816MB.
• Running two in the same client maximum RAM is 2304MB.
• Running all three in the same client maximum RAM is 1792MB.
• CrossfireX works when running both GPU's on the 4850 X2 in the same client.
• I can assign and use each gpu on the 4850 X2 in separate Windows clients.
• HDMI sound works on both 4850 X2 GPU's, not tested on the 2600 XT.
• The original Windows driver for the 4850 X2 gives blue screen at boot, have to boot in safe mode and disable the adapters, reeboot and then install AMD Catalyst drivers.
• Looks like DXVA does not work on the 4850 X2, not tested on the 2600 XT.

Also found working with passthrough:

• SAS-controller: Fujitsu D2607 (LSISAS2008 based)
• Graphic adapter: Asus (ATI) Radeon X800 XT 256MB (PCIe)
• Storage controller: onboard VIA ATA133 controller

Found not to work with passthrough:

• Audio adapter: onboard (Windows freezes at boot)
• Graphic adapter: Leadtek (NVIDIA) GeForce 6200 TC 64MB (PCIe) ("This device cannot start")
• 1394 controller: onboard VIA ("This device cannot start")