A lot of that momentum comes from the fact that Linux is free.
There are a lot of people who've been able to ditch their Windows machines and switch over to Linux because they can now use their Exchange server for calendaring and collaboration from their Linux desktop.
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.
Linux is a cancer that attaches itself in an intellectual property sense to everything it touches.