Something like 28800 pixels on typical monitors these days?

So programs will make their basic functionality more discoverable instead of hiding it in the menus? And when only less-used functions are relegated to the menus, there's not much point in having them visible all the time. There will be a larger contrast between common, discoverable functions and rare, hidden-away ones.

Looks less cluttered? It is a design decision so you're not going to get a universally accepted answer.

It's good for netbooks. That being said, I've got 11.04 running unity on the mother of all netbooks, the original eeePC 7". I click on the application finder and it is too large to show the search box on-screen - there's no intelligence; instead of showing one line of icons and the search box, it shows the stock two lines and kicks the search box offscreen.

I have unity on a VM on a 1920x1200 screen as well. Here I have a lot of screen-estate... and the interface is too small, really. On such a large screen, when I want to interact with it, it's too much out of the way.

So, in my experience, unity isn't for large or small screens.