"Linux" is not difficult. In fact, I can make the case that it is easier to use than Windows. The learning curve may be steeper, but the ease-of-use once you have learned it, is better.
When you're talking about ease of use though mostly you're talking about learning curve. Something with a steep learning curve which is easy once you figure it out is what we generally call "expert friendly". Expert friendly isn't entirely a bad thing, it's good to have strong features for power users, but if you want to bust into the mass market you need a shallow learning curve that eventually leads to power user capabilities for those that want to dig that deep. To rule the desktop world you need to get as close to possible to appliance level of initial usability, pretty much anybody that's ever heard of a microwave or toaster or Foreman grill can take one out of the box and cook something with it in the first 10 minutes. Really Mac has consistently come the closest to that, depending on who you're buying from pre-configured WindowsXP comes in anywhere from a close to distant 2nd, Linux and company are sitting near the bottom slightly easier than Win3.1 (which had some horribly counterintuitive things about it). But they're improving the Linux variants, the hard part is keeping the power users happy while dumbing down the first 10 minutes, seems like they're on the right path though.
Did you mean to indicate that it is a more difficult to learn?
A steep learning curve would indicate that something is relatively easy to learn.
Not true. The "tree view" portion that works like "Windows Explorer" is much more difficult to navigate, you can't just click on most "exe" files and have them start right up (most require command line activation) and installing 3rd party software can lead to ulcers.
My wife and kids (all MS users) pretty much refuse to use my Linux PC because they find it too daunting, yet they picked up Windows right away.
Having said that, I find Linux to be a pretty good operating system and it's "bundled" software is much more plentiful than Windows. There are the above mentioned problems but only the "dependency" issue is totally frustrating.
Linux is close, but not quite there yet. The future for this OS is limitless.
I've got people asking me about my Live CD--I run it at school in the library. It is instances like these that the Joe Sixpacks can get some exposure to Linux--like I've been saying, we need to get the word out to people. And one of the easiest ways IMHO is to let them experience Linux firsthand.