It's interesting to talk to people in this business and find the religious fanaticism that revolves around the support of different hardware vendors. I've met systems people who have variously sworn by HP, Dell, and IBM. But what about the good old white box? If you look at it closely, a lot of businesses are throwing away good money for name brands when a white box machine could be built with the exact same chipset for a lot cheaper.
For example, we do a LOT of work with VMs here at 3Sharp. I built us a VM server with 2 quad-core Xeon procs (2.2Ghz), 32GB of RAM, in a 1u form factor with mirrored 500GB SATA 2 drives. This server cost about $1750 to build, a server from Dell with the same chipset, procs, RAM, and HDD costs $6911, and if I were to switch it out with Opteron procs, the price would still be $5196.
The objections to this approach to hardware generally tend to revolve around convenience and support. My take on it is that if you can save 40-70% on your hardware costs, you can then easily afford to have spare parts for every system you have on hand. That also means that you can have a better response time than the 4-hour onsite.
There are a few keys to making this work though. First, you have to have at least one IT staff member who REALLY knows his hardware. This means knowing when a 20-pin power supply will be able to power a 24-pin motherboard and not void the warranty (the answer is that if you're not going to be putting in a lot of add-in pci or pci-x cards, you should be ok). Second, pick a standard. If you're whiteboxing your servers, that means you settle on one or two motherboards to be your standards. The less variety you have, the fewer spare parts you'll need to keep around. Third, pick your vendor very carefully. The best price is definitely not always the best deal.
Other keys to success with whiteboxing include using a good system monitoring solution. We use Microsoft SCOM, but I've also used Nagios with good success. I've also seen comparable reliability to brand name servers with the units I've built here.
While it may not be practical for large organizations to use whiteboxing, small to medium sized businesses can benefit greatly from it. Their IT staff will be much more intimately familliar with the hardware, and costs will be reduced.