OS X has, since 10.7 Lion, a "native" way for apps to go fullscreen. It is represented by two arrows at the top left of the window.
Using this kind of fullscreen has the advantage that the normal OS X shortcuts to switch windows still work, and when the new OS X 10.9 is out, it will work even better, allowing users to have other windows on a second monitor still visible.
I'm sure someone around the office is using OS X so they should be able to tell you how it should work 😉
Java applications can use this native fullscreen as described in this SO thread: http://stackoverflow.com/questions/6873568/fullscreen-feature-for-java-apps-on-osx-lion.
Applications that provide this feel more "at home" on the OS X platform and have, imho, a better user experience (especially since your current fullscreen mode disables the default osx shortcuts and blacks out other monitors), so please consider doing this 🙂
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Duplicate of MC-26102, please use the search function to see if your bug has already been submitted. Currently over 58% of tickets are being resolved as duplicate.
LWJGL does not currently support OS X native fullscreen.
You might want to comment on the linked thread about your solution.
As a side note: Applications that use this usually show the menu bar (with a button to go back to windowed mode) when the mouse is moved to the top of the screen. This should only be possible in menus or when the game is paused for minecraft, methinks. Then again this may be a system behaviour and require no work at all from your side.