By contrast, without plugins, Unity's launcher remains fixed on the left side of the screen. The size of its icons is also fixed, and its context menu tends to have only the most common options available.
However, unlike OS X's dash, Unity's launcher does double duty, displaying open applications as well. It does this with an elegant economy, indicating open apps with a left arrow, and the current app with the right arrow.
Both the launcher and the dash struggle with space limitations. The problem is especially acute with Unity's launcher, which is scrollable and uses semi-collapsed icons on the bottom to save space.
But, unfortunately, the ingenuity of this widget is marred by the fact that identifying the collapsed icons is difficult. On the whole, the widget is far less successful than the spinner on the OS X dash. Creating a wheel of half a dozen enlarged icons anywhere along the length of the dash, a spinner is far easier to read than Unity's collapsed icons.
Despite some innovations, in the end, Unity's launcher is a simplification of OS X's dash. The simplification makes Unity far less intimidating than OS X's dash, and probably quicker to learn. However, experienced users, I suspect, will find OS X's dash more flexible and adaptable to their individual needs.
The divergence of menu replacements is the second area where Unity and OS X converge. This is a problem that many desktops struggle with, and Unity and OS X are no exception.
If you can't find an application on the launcher or the dash, both Unity and OS X provide alternate tools. In the simplest case on OS X, users enter the application name in the Spotlight field on the top panel. If that fails, they can open the Finder, a combination of file manager, menu, and system bookmarks with a variety of views. The Finder looks like it could have been designed a decade ago, but is a powerful and centralized tool.
By contrast, Unity relies on its dash, a screen-wide replacement for the menu. By default, the Unity dash displays Recent Apps and Recent Files. However, results can be limited by lenses – predefined filters -- or by entering text in the top search field, with auto-completion suggestions changing as you type. The Unity dash has no system bookmarks, although immediately below it on the launcher is the file manager.
Functionally, OS X's Spotlight and Finder and Unity's dash are approximately equivalent. Unity's dash is more visually sophisticated, but, against its power and ease and use is the fact that it occupies the entire screen. Despite a transparency effect, opening the dash means interrupting what you are doing in a way that using the Spotlight and Finder do not.
The dash would probably be effective on a mobile device, where such interruptions are the standard. However, despite their lack of polish, the Spotlight and the Finder are less of a distraction when you are trying to concentrate, simply because they don't remove you from the screen.
In his 2012 keynote, Shuttleworth also mentioned the Head-Up Display (HUD), which replaces traditional menus with field completions as you type. However, whether HUD should be taken as an example of Unity surpassing OS X at this point remains doubtful.
HUD is a work in progress, and, to take it too much into account at this point seems, unfair. But, in its present state, it is an even more annoying interrupter of productivity than the dash because it is much slower to use, and has no means other than trial and error to search for a particular item.