I'm surprised at how much I like Ubuntu Linux better than Windows! The UI is basically the same, only everything is faster. Especially when you do anything to a file (write to it, read from it, move it, or delete it), Linux turns hours into Minutes. When you consider that doing anything useful on a computer generally involves changing a file, that says a lot!
Printing to a network printer was actually easier on Linux. Our vendor-supplied proprietary Windows driver hangs the printer every second or third time you try to print a PDF! I've got my complaints (a few sound limitations and a few software packages that I still have to run in a Windows VM). But whenever I have to fix someone's Windows computer I pity them. Even Windows runs better on Linux (in a VM). That way you can keep working while you reboot, reboot, reboot...
As I'm writing this, I can hear my wife downstairs using Windows... "Network Problems!?! I can't have network problems right now! Operation failed???" I feel sorry for her, I've been there myself, but I have to laugh at the background to this blog post.
I encouraged some people I know who are absolute beginners with computers to buy Macs. But now I'm not so sure. Ubuntu Linux is actually easier to navigate in some ways than a Mac.
Update 2010-04-01: I spent 2 hours trying to copy some pictures from a camera to the hard drive on a Mac and it was awful. In Ubuntu, your camera gets mounted as a drive and you can drag and drop the pictures wherever you want them.
The only drawback to running Linux is that some programs only run on Windows. Screen sharing programs (except for TeamViewer) all require Windows or Mac. The latest version of Microsoft Office only runs on Windows, Photoshop only runs on Windows/Mac, and Proprietary VPNs only run on Windows. Most people don't need those things, but I do, so I have to run Windows in a Virtual Machine. But I only have my VM running about 25% of the time.