Comment 25 for bug 648180

Well, it does save screen real-estate for small screened devices when working on a few full-screen applications.

Unity might make sense for screen heights of 768 or lower.

On my laptop, where I'm currently alternating between Unity (trying hard to like it) and Gnome Classic. Even if I don't autohide the menu in Gnome Classic, so it burns 20px, and use one of the default themes instead of one with a thin upper menu, a maximised Firefox window has 695px available to the page. (and yes, I customised a bit. That could be default for smaller screens, but even my linux novice mom figured out how to do something like this on her own)
http://m8y.org/tmp/Gnome.png

Now in Unity, that jumps to 718px available to the page, but at the cost of losing half the functionality of the top menu. I'm not thrilled about the cost of those 23px, esp since I could reduce that with a different theme.
http://m8y.org/tmp/Unity.png

Now if only patches were submitted to Gnome to allow apps like firefox to do what they do under windows and put tabs/firefox button on the same line as windows chrome, then I could keep my main panel functionality *and* save the pixels.

The other thing I like about Unity is the spotlight search feature - that is quite nice. Hopefully it'll be pulled into Gnome.

The app menu is a "meh" - such things have existed for gnome, I never found them useful enough to leave active.

So. Saves a bit of vertical space at the cost of features, and has an awesome search. There you go. Positive stuff! :)