No, not maximise, full-screen. Subtle but important difference. Checkout what Firefox or Chrome do when you hit F11: window covers the whole screen, including the panel, and window borders and title bar disappear. You get absolute maximum use of the screen. I use a netbook with 1024x600 resolution, so it's really important to use every pixel effectively!
Not all apps support F11, but Metacity can do the trick with any app, normally mapped to Alt+F11. That's what I'm looking for, I can't believe other WMs don't support it.