I'm using Ubuntu 10.10 UNR now. The Unity interface is a huge step back from the previous UNR interface. Just simple things like launching a different application for a file can't be done (eg, to edit a photo rather than view it). You can't pick up a file and move it to the trash.
The interface reverts to the top view after each application. So if you want to do the same thing to multiple files you are always navigating back to where you just were.
The list of applications takes a huge chunk of small-screen real estate, all the time. The previous interface assumed that if you selected an application, you wanted to focus on it for a while and didn't mind a click to get back to the main screen.
I still haven't figured out how to add programs to that list of applications. So I have to use the application picker. Which is a rip off of the MacOS one, and one of the least thought out aspects of MacOS. MacOS rescues the situation by putting the application on the task bar, but Ubuntu doesn't do that.
The combination of these flaws is that it can take more user interface interaction to launch a program than to do the work of the program.
It's just not ready for the big time on the small screen. I'm looking to see what Fedora might have for Netbooks.