Space bar is one of its kind. Then come three others: regular key, middle-size key, and double-size key. That's it.
Here's the preview of what we'll show at CeBIT this month (to be released in the end of 2007):
Return and Shift are double-sized, Alt and Ctrl are medium sized.
← Ctrl ← Alt
Ctrl → Alt →
← Ctrl ← Alt
Ctrl → Alt →