Unity isn't going to drag any joe-average users to suddenly want Linux on their PC. It's neither consistent with what their used to nor does it create any kind of superior paradigm to what already exists.
Sure you can browse the web , play music and do the odd spreadsheet etc with it , big whoop we've been doing this for years , it would have been exciting in the late 90s not now.
The barrier for Ubuntu is not really it's UI. It's problems like having a really horrible flash player, poor selection of applications for many tasks (not to mention games). Not to mention other nasties like pulseaudio,networkmanager,dependency problems etc.
Ubuntu is so desperately trying to be a cut price apple, now they want to move to tablets.. Ok so they will have the same problem they have had on the desktop for the last 20 years, lack of consumer applications.