Hide application menu bar

How can I hide the Menu Bar? I am on mac Osx moutain Lion (10.8)

Yes, one can full-screen an app, but it does not solve my problem. Here are 2 scenarios to explain my problem:

Scenario 1:

I am running macvim in one space and Chrome in another. Chrome by default 'merges' it window top bar with the tabs, but macvim does not. So, on my macvim I can see both the menu bar and the window's top bar. While chrome's window is indeed useful (It contains tabs..), macvim's top bar is useless. All the info is in the powerline I'm using.

Scenario 2:

I have 2 displays, full-screen apps appear only on one screen and there is no way to have another app on the other screen (Unless if I missed that!). So I'd rather have, again, macvim on the first big display and chrome on the small one. But then again, macvim's window topbar is here, taking useless space.

I hope I made the point clearer!

You can make the menu bar of an application hide automatically by adding this to the Info.plist:

<key>LSUIPresentationMode</key>
<integer>4</integer>

Windows can't be moved over the freed up space though.

If the application is signed, modifying the Info.plist invalidates the code signature. It also makes sandboxed applications like TextEdit and Chess crash on launch.