I ran Linux (Red Hat) exclusively for 5 years. Both on the desktop and server. I used WindowMaker as my window manager.
Linux is great, however, I had to move to Windows (2K).
Why?
Linux simply does not have a stable web browser that will run several java applets simultaneously, macromedia, audio/video plug-ins, etc.
If I had $1 for every time I had to ps -a | grep -i netscape, kill -9 [netscape process], I would be a very wealthy man. Netscape/Mozilla on Linux doesn't cut it stability-wise. Yes, there is Opera and Konquerer, but I work with alot of media rich, plug-in laided, java-oriented broweser apps.
These days, for many people, the browser is the operating system. The OS is becoming irrelevant, they just fire up the browser as soon as they turn the computer on. Linux does not have a *truly* stable browser, and thus for many people is much less stable than Windows.
It's the best server in the world, and I miss the free tools (C compiler, etc) - but until something even remotely similar in function and stability to IE for Windows is released ... it is not a viable desktop, IMHO.