http://www.netcraft.com/survey/
Microsoft will beat Linux at clustering? As load balancing aka clustering is done at the TCP level, it's irrelevant. It's possible to cluter Linux and Windoze machines in the same farm.
The adult industry colocates with a much higher frequency than any other net industry I've been involved in, and Windows just isn't as convient to remote-admin via GUI as a UNIX machine is via SSH.
Anyone play with Apache 2 yet?