This quote from Michael Dell's interview is pretty interesting:
MD: "The interesting thing is when we design and architect a server, we don't design it for Windows or Linux, we design it for both. We don't really care, as long as we're selling the one the customer wants. If a server goes down the production line, it doesn't really know what OS it has on it until the customer says, I want this OS. It could be Novell, SUSE, or whatever. "