Since Windows 3, third party developers have been producing GUI extensions and replacements that give users quicker access to applications directly from the Desktop. A popular metaphor has been the launcher bar. This is a bar with buttons bearing iconic representations of the applications they give one click access to. Indeed in Linux several of these launch bars or 'docks' exist and are popular, these include Avant Window Manager, Docky and Cairo-dock.
There is nothing strikingly modern and new in Unity despite what you may have heard. What the interface does pioneer is a move further from the Windows Interface design model and closer towards an Apple style design. Why? Perhaps the explanation is that at heart Unity is the development of a multi-touch interface. For multi-touch read touch screen. It may seem logical to Canonical to design a unified GUI for their operating system on every platform. The major player in the tablet market, indeed the company that resurrected and invigorated the form factor, is Apple, so Unity borrowing heavily from a Mac-like design brief hardly seems surprising. To rest any share of the dynamic new tablet market Ubuntu must convince that market that it can deliver a user experience at least as good as Apple. Even then it is unlikely to be enough, unless Ubuntu can outperform Apple and deliver a compelling reason to opt for anything other than an iPad then the tablet market will remain effectively monopolized.
It may seem heretical, but I have no objective issues with Microsoft's interface design. My objection to Microsoft is their closed and proprietary source, their patenting of software and their curbs on freedom and innovation. Using Linux is, for me, a political decision to support open source and object to the restrictive practices of closed source. I have no problem with Windows as an operating system, it's unquestionably very good. There can be no argument with it's compatibility with all major hardware vendors. Given that Microsoft have spent many millions designing an interface that is logical and intuitive, especially for new users, building an interface designed, in principle, on the way in which Windows works can only be a good thing. As most of the world think of the computer operating system as Windows, surely an OS that presents a radically different interface will not be attractive, especially those migrating away from this software model.
This leads to my main point. Who is Unity for? If it is for the existing Ubuntu community? Then why make such a divisive and sudden conversion to a brand new interface that no one is familiar with? It's not that long ago when one of Ubuntu's core attribute was being primarily a Gnome desktop environment (DE) distro, this meant a Gnome 2 panels DE. Now, though still a Gnome distro, it's ditched the panels and eshrewed Gnome Shell to present a completely new DE built on Gnome. What the hell is wrong with Gnome Panels? If Ubuntu is to continue the process of drawing new users across to Linux then their target must be Windows users. Given this, why take the interface design in a direction away from that which Windows users are familiar with toward a more Mac-like experience? Is Unity aimed squarely at tablet and smartphone users? If that is the case why should Unity be useful to a desktop user in a mouse driven environment?
There is actually nothing truly fresh and innovative about Unity and the mulit-touch design principles will not win over Windows users or even users new to the Desktop market and is unlikely to win many adherents in the tablet market. So the question who and what is Unity for may become a millstone around Canonical's neck.