Unless the interface is just completely broken, I think anyone can get used to a new product after a few months.
Windows 8's (and to a lesser extent, Unity's) problem is that it presents a new user interface paradigm, but doesn't guide the user through the new interface. As such, the user ends up not being able to do familiar tasks, and grows frustrated in a way that colors their entire perception of the product.
In contrast, the first time I powered on an Android smartphone, I was greeted by a tutorial widget that got me up and running quickly with the home screens, widgets, app launcher, and app market. Android may have its frustrations, but not knowing how to use it isn't one of them.
Tutorials/guides -- even if it's something as simple as brief video tour -- pays dividends in first impressions and overall satisfaction. It blows my mind that they are so often ignored.
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