I would consider paying for .net if it received first class treatment on Linux. As someone who has lived through the pain of hosting apps on Windows, I just refuse to do it in the future. I'd love to see Microsoft bring Mono into the fold and truly bring it to the level of the Windows .net implementation.
Linux works great as a server OS once I get everything set up and configured correctly. I never need to think about it again. However, I dread having to set things up on a new Linux machine. There's always some hardware that doesn't install correctly or some config file that needs twiddling. Sometimes it takes an odd sequence of commands that needs to be run in just the right order to get things going. Invariably I waste hours on the internet searching forums every time I do this, getting more and more frustrated the whole time.
As far as Windows hosting goes, I find IIS 7 to be much easier to set up and customize than Apache in terms of hosting web applications. I find the uptime of Windows Server boxes to be functionally equivalent to their Linux counterparts. I also find it's much easier to administrate large groups of Windows servers because of the nice tooling. Things like Active Directory, SMS and SCOM make things pretty easy.