While Ubuntu's Terminal has a full-screen mode, there is nothing similar built-in to OS X's Terminal. If you need a distraction-free UNIX environment (not unlike previously mentioned WriteRoom for writing), here's how to get a full-screen Terminal session in OS X.
While you could always just maximise OS X's default Terminal app, it's not exactly purely distraction-free—dock badges, Growl notifications, and all sorts of other things sill lurk in the background to draw your eyes away. If you do a lot of terminal work, reader Ian has written a blog post documenting a few mods to X11.app will get you running xterm full screen.
It does require a bit of prying into system files an the like, but if you're the type that would need this mod, it's probably nothing that you wouldn't already be comfortable with. You'll have to edit X11's plist file in ~/Library/Preferences, as well as setting up your own .xinitrc file to launch your terminal. You'll also probably need to do a bit of trial and error to get it to fit your screen correctly (since you have to manually define the dimensions), but again, it shouldn't be too difficult for those familiar with Unix. Hit the link for the full instructions.
Full Screen Terminal in OS X [hccp.org]