Like all Apple keyboards, the iPad keyboard dock has a row of useful buttons along the top row, controlling such things as music playback and screen brightness. The iPad has these, plus a dedicated home button, a key to start a photo slideshow and a search key. But, smack in the middle, there's a blank key, a mystery button with nothing printed upon it.

The mystery key was noticed by Mac Rumors forum member Macduke, who posted the above image. He speculates that it may gain a function before shipping, and that function would be to invoke a Mac-like dashboard, complete with widgets (which would be great, by the way, especially for quick Twittering). I checked around the web to make sure that the blank key was indeed blank, and plenty of hands-on shots also have the mystery chiclet.

So what is it for? Any idea is pure guesswork, but I certainly like the dashboard theory. It could also be a user-customizable key, or an unlock key for the screen. My guess? The mystery key will turn on the non-existent camera. Put your ideas in the comments.

iPad Keyboard Dock's Secret Button [Mac Rumors Forums]