My whitebox: AMD, 8GB RAM
My whitebox has been up and running for quite some time (since ESXi 3.5) and I currently have ESXi 4.1 installed.
ASRock ALIVENF6G-VSTA AM2 NVidia 6100 Motherboard
AMD Athlon X2 BE-2400 Brisbane 2.3GHz
Intel Pro MT 1000 NIC
OCZ 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (x2)
PROMISE SATA300 TX4 PCI SATA II Controller Card
Seagate Barracuda ES.2 ST3250310NS 250GB 7200 RPM SATA Hard Drives
But does not support vt-d (directed I/O) / AMD IOMMU
USB passthrough works.
The 8Gb of RAM is my main limitation as I have about 20 virtual machines installed (only half of them are powered on at one time though).
I am starting to think ahead for a new build - I am happy to try and stick with AMD but will switch to Intel if I can get a board that supports 24Gb or 32Gb of RAM and VMDirectPath - with this I plan to consolidate 3 machines into one if I can (current ESXi Server, Media Center and Windows Home Server).