I've disabled bookmarks, status bar, search box, back, forward, home buttons.
Rationale:
Trying to shift everything to keyboard based navigation. Bookmarks are mouse based and aren't that much faster then typing thanks to the Firefox 3 "Smart Location Bar." The thing is awesome. It seems to know when you want a google search and when you just want the website, and it gets smarter the more you use it. It pulls up results from history (which I am trying to preserve rather than delete to save space) and bookmarks. The shortcut is ctrl (cmd) + L to jump to it, which is very natural to use since you have two hands on the keyboard to type anyway.
Backspace sends you back a page, so I don't need the button. My normal home page is just google, which I don't need anymore thanks to that location bar. The extra search box is made obsolete by the location bar as well.

I've also downloaded a little app called Launchy, which is quite similar (though not as comprehensive or feature rich) as Leopard's spotlight. I can, however, simply launch Firefox with a Alt + Space + F + Enter, because it is the first result. More on Launchy later.
The lack of any of those bars leaves me with only the standard menu (File, Edit, etc), the Location bar, and the Tab bar, which fit nicely on two lines (see screen).
I've also given the status bar the boot, considering it really doesn't do much anyway. Just that simple "Done" and a lot of empty space.
Also of note is the shortcut to switch tabs, which is quite useful to a keyboardist. A quick Ctrl + Tab moves along the line. Other tab shortcuts of note: Ctrl + W will quit that tab (or close the window if you are going tabless) and Ctrl + T creates a new one.
End result: much more space for browsing.