Linux Advantages (as I see them):
1. gives you more control and freedom. no annoying popups telling you to do this or that.
2. no activation and reactivation BS after changing a piece of hardware.
3. more choices in desktop environments, window managers, etc.
4. less prone to virus and spyware problems. install linux and you're good to go, install XP
and you're really going to want to also install service packs, a virus scanner, and spyware
cleaner.
5. can be more efficient with your system resources and will run faster, if configured properly.
6. mythtv = free and is at least as good if not better than Windows solutions like BeyondTV,
GBPVR, etc.
7. Linux is a free download. Ubuntu won't even cost you a cd-r if you order it from their
website.
8. Allows you/forces you to learn more about your hardware and the OS itself.
9. OS is free and won't even cost you a cd-r in some cases (Ubuntu will send you a free
CD if you request one on their website.)
Windows Advantages (as I see them):
1. still has more/better hardware support
2. still the better choice for gamers
3. easier to install and remove applications, drivers, and etc. (although apt-get and the like
are making things easier under Linux).
4. still may be some software with no real equivalent choices under Linux.
5. in general Windows still is easier/requires less time to get the OS, apps, and drivers
installed, configured, upgraded and tweaked. Those w/o the time or desire to work on such
things may not like Linux.
I've looked into Linux as a desktop alternative periodically over the years and have to say that I've become increasingly impressed by its improved capabilities, stability, and performance. Years ago, I remember trying Linux with a window manager and a browser like Netscape or Mozilla and recall how bloated some programs were, how slowly the browser loaded, how poor the interface was, and etc., when compared to Windows at the time. Today, I can comfortably say that Linux, especially with a Window Manager like XFCE, or even a desktop environment like KDE or GNOME, and a browser like FireFox, can perform at least as well, if not better, than Windows XP. Multitasking seems to have improved a good bit under Linux... perhaps its multithreaded performance has improved over the years or something else has improved because I used to find multitasking somewhat lacking when compared to Windows... it just wasn't as smooth but now it is, if not more so. Installation is also easier now than ever before. With distos like Ubuntu, you got yourself an excellent fully working Linux Desktop that is as easy if not easier to install than Windows XP.
If you're not a hardcore gamer, can live with things like nVidia video drivers that are somewhat less full-featured than their Windows versions (I can't seem to enable 32-bit color), find the current Linux hardware support adequate in covering your needs and can live with waiting for new hardware support to trickle down from Windows, and can find equivalent Linux alternatives to the software you use under Windows, then Linux today has become a truly viable alternative for the desktop, in my opinion.