the only consensus i'm seeing is that everybody wants to hate ubuntu. a mainstream product is the perfect place to test new UI concepts, because mainstream users don't care about these things and they don't have any expectations. despite what you might think, being very similar but not quite windows is not a good thing for a mainstream user.
everybody i've tested unity on has adapted to it really quickly. the very basics need teaching (things like showing them how to open the launcher), but beyond that users are pretty good at discovering things for themselves. the problem with making things very like windows is that people expect it to be exactly like windows, and panic when something isn't where they expect it to be. unity removes expectations and the user starts off with a blank slate, and they can learn fairly quickly. also, mainstream users don't panic over change they way you imply they do. they just don't notice change. there's a presentation from google that mentions when testing google instant, many users didn't even notice anything different.
the people who are hating on unity and ubuntu are not speaking for the mainstream, they are speaking for the power users who have a library of learned behaviours that they don't want to unlearn. a mainstream user doesn't have a whole lot of learned behaviours to overcome, and they will benefit more from a UI improvement than any other because so many of them are essentially re-learning the system every single time they try to accomplish something. lots of people say they want ubuntu to be built for the mainstream, but what they actually mean is that they want is a distro built specifically for themselves.