Ben,
ASP.Net is now available on Linux, via the Novell's Mono ptoject, currently at version 1.2:
"
Mono provides the necessary software to develop and run .NET client and server applications on Linux, Solaris, Mac OS X, Windows, and Unix." http://www.mono-project.com/Main_Page
Microsoft's Silverlight (alternative to Adobe's Flash) will also be available for Linux, via a partnership with Novell.
Myself, I'm a Windows platform developer, but not for technical reasons, rather because my initial programming experience was with VB. I don't claim one OS to be superior to the other. I couldn't anyway, since I have no Linux experience. I find the most informative comments are from those who have extensive experience of both.
James