My wife has used Ubuntu on her Dell laptop for over a year now (since Gutsy was released), and she can't figure out bittorrent on Mac, Windows, or Gnome, but using Nautilus for sftp doesn't phase her. I think the single biggest drop in user comfort occurs whenever one application launches another application. Other anecdotes come from finding computers in hospitals with bad Windows images. I load an Ubuntu CD and observe. Docs come in, and use Firefox. No, they can't get their specialized clinical apps, but they have no problem using the same app in a different OS. Similarly, they almost universally either use Macs or are acutely interested in making a Mac their next laptop (I heard once that 40% of docs use Mac).
I think the idea that everyone will use Linux is not so distant a reality as a lot of people think. I'm not in the IT industry. I'm a military doctor. People know about Linux, and they're intrigued. Now. Right now. And more are learning every day.