OS X does the same thing. It has a launcher on which you pin the most used apps and for everything else you need to search it with Spotlight, or go to the Applications directory in Finder. I haven't seen many people complain about the usability of OS X in this regard. IMHO, the Start menu is a broken abstraction.
As for the UI and that bullshit on being optimized for tables ... I actually like that Unity is so space efficient. For example, why in the world would I need a window top bar, if the window is maximized? Vertical space on 16:9 screens is precious, Unity optimizes for it and I find that to be awesome ... like, one of the reasons many people like Chrome's UI over Firefox is exactly because of this, yet Unity brings this design decision for all apps.
- remove cascade style start menu.
- quick search interface for application, files.
- well organized keyboard shortcuts and inline shortcut help
- make free vertical space as possible as
- it's simple. users only need to understand windows key, left launcher.
Yes, It was buggy and slow at the first time. Maybe Canonical had pushed so much earlier. But it's now working well and really usable.
The UI is optimized for tablets and phones, but not because of space efficiency. In fact, Unity is less space efficient, because it demands that the launcher be so huge (to afford touch-based interaction). In every DE I've ever used, I actually hide the top/bottom panel, but that's not possible in Unity (the top panel affords no customization whatsoever, AFAICT). So, in practice, Unity is consistently less space-efficient with my vertical space than every other DE, in addition to being less customizable.