First, I took several of my Windows systems and tried to upgrade them to Windows 7 Ultimate. It was ... interesting.
Coming from Windows XP, I found, as I expected, that there is no easy way to upgrade. The only method is what Microsoft calls a "custom install" and what I call a slash-and-burn install. In the end, you'll have to let the Windows 7 installation DVD delete everything on your hard drive.
Microsoft provides a tool, Windows Easy Transfer (aka migsetup), on the Windows 7 DVD that will transfer files and settings to an external drive. This is a pain in the neck, but it does work. What it doesn't do, however, is transfer programs, fonts, or drivers. Once my Windows 7 was set up, I had to reinstall every last application, font and driver. I couldn't believe that a modern operating system actually made it so hard to upgrade it.
Still, it is from Microsoft, so perhaps I shouldn't be so surprised. What did surprise me was that I found I couldn't update the Windows 7 RC (release candidate) to the RTM (released to manufacturing) version of Windows 7. The only version of Windows that can be upgraded without jumping through hoops is Vista. Even Vista, however, can only be upgraded easily from the same version to another or to Windows 7 Ultimate.
For Linux, I upgraded from Ubuntu 8.10 to 9.04. In stark contrast, Ubuntu was easy to upgrade. There's simply no comparison with Windows. Linux has the undeserved reputation of being hard to use. What a joke! Most users will have a far more difficult time upgrading Windows.
I prefer Linux for most desktop uses, but I confess that Mac OS X Snow Leopard is also an easy upgrade. Just like Ubuntu Linux, all you really need to do is put in the DVD, make a few mouse clicks, and go have lunch while it runs. Snow Leopard, on my Mac mini, took just over an hour to install, and about 45 minutes on my MacBook Pro.
Once installed, both Snow Leopard and Ubuntu ran perfectly. That's more than I can say about Windows 7. After installing it, I found that an old Vista networking problem with working with NAS (networked attached storage) was still present and required me to manually adjust an obscure local security setting. Windows is easy? What nonsense!
Linux, it must be said, took less time to install than Mac OS X. But, really, there was no practical difference between Snow Leopard and Ubuntu 9.04 in their ease of installation. So, when it comes to being easy to install, I see it a dead-tie between Mac OS X and Linux. Windows? It's far, far in the back.
But I guess I can't complain too much. I'm sure I'll get to write a few "How to install Windows 7" stories, which is more than I will with either Linux or Snow Leopard. Of course, if you're a Windows user, you'll certainly have a lot more trouble but hey, it's your dime and your time. Spend them as you wish.