Linux is great for servers. For a desktop OS... 
Though I should say Linux can be a great desktop OS for someone who is really technically inclined and wants to learn their OS in and out. The ways in which you can customize it are unparalleled by Windows or Mac. But even I have limits on just how much time I like to spend tinkering 
The thing about linux is that it's "new". Same thing with the Mac, it's something "new" so for some people, like me, it is exciting to learn something new and tinker with it. I was one of those kids that would take apart the alarm clock to see how it worked.
Linux works great as an embedded system where you won't be installing a lot of new programs from all over the place, such as say Google's Android. Everything you install comes right from one "app store" and installs in the same way. On the desktop, you have RPM based distros such as Red Hat and Mandriva, Debian based distros that use .deb files, some have package management tools like apt and yum with front ends like Synaptic, and sometimes you can only find the app you want in a g-zipped tar ball, package.tar.gz where you would have to go into a terminal program and do commands like
# tar xvzf package.tar.gz
# cd package
# ./configure
# make
# make install
Since both are unix based, I don't know why linux distros wouldn't come together and implement a system like OS X uses. Applications come as a file like "firefox.app" where the .app file is really just a folder that contains the executable and all related files. To install it, you just drag it into the "Applications" folder or wherever you want to keep it. To uninstall, you drag the .app file to the trash and empty the trash. No command line, no tarballs, no package manager required.
In fairness, Dell would not be on the top of my list of preferred PC makers. But that's mostly because I'm biased against their awful touchpads.
I love the silky smooth glass multitouch trackpad on my MacBook Pro
Wow, that Koolaid looks superior to the koolaid I can get at Food Lion. It is definitely worth the $0.20 instead of the crappy $0.10 stuff at the supermarket!
