I knew as far as usability goes, Unity would be great for new users. Much simpler desktop, type the application instead of visually searching through a hierarchy, etc.
But I thought the desktop was too simple for someone more advanced who knows all the shortcuts by heart, uses widgets, etc.
Nevertheless, I gave it a try and now only 2-weeks later I can never go back.
I have the same experience with Google Chrome. I missed some of the add-ons and features in Firefox so first I didn't bother with Chrome. Then I tried it and switched back. But now I prefer the simplicity of Chrome. Even now that Firefox 4 has far too many usability improvements over the previous versions, I still prefer the simplicity.
If you use Ubuntu, don't be afraid to try the new Unity interface. You may just like it. I would also recommend some of these Unity tweaks to help your experience a better one.