Soon enough Ubuntu will be pluggable to our tablets and smarts or whatever hybrids will come forth in the next years.
Was Unity specifically designed for a tablet? Does the window system have multitouch support? Accelerometer support? Do any of the applications themselves support multitouch and accelerometers?
Though, in a couple of years, who's to say that Ubuntu won't be able to run on most devices? Maybe there are challanges, but I doubt that it would be impossible. It's just a matter of time and maturity.
I think people are already asking for one user environment across devices, so I bet it's something they might have in mind.
But I see no reason a Mac user would find Unity more attractive than the Mac UI.
If they'd copied the Mac UI exactly then they'd have achieved parity.
If they'd done their own UI research and come up with something new, they might have been able to come up with something better than the Mac UI. Certainly there is some room for this, given Apple's need to support old paradigms. But if you've noticed, Apple isn't exactly nostalgic.
But by copying the obvious ideas, but not thinking thru why Apple made the choices they did, they miss the mark... which seems to happen with everybody who tries to copy Apple's innovations. They end up with something that on the surface looks the same, but doesn't actually work the same.
I think this is because its too easy to "improve" what Apple did based on their preferences, without understanding why what Apple did the first time was the right way.
Given that linux has a much higher cost[1] than OS X, to gain a lot of market share, it will need a much better UI. We saw how things went for Apple for many years, despite having a much better UI (and cheaper machines, actually) than Windows...it wasn't until the iPod lowered the awareness cost that people started switching to Macs in droves.
[1] Not all economic costs are measured in dollars. Lack of awareness of a product creates a barrier of entry, and while many people have heard of Linux, few are aware of it as a Desktop operating system. This lack of awareness is a cost that needs to be overcome, or reduced, to get a lot of switchers.
IIRC, the Unity team has been actively doing user testing, and there have been several changes in the UI as a result.
BTW, I had trouble adjusting with Unity in 11.04 but I lived through it. Now, I don't find it troubling at all and this is the longest streak I've been using Linux without moving back to Windows. For me, 11.04 might not have been a game changer but it was a great foundation. 11.10 is updating on the background and I can't wait to check how Unity has turned up.