I think another approach might be to reconsider the keyboard.  the device still looks to me like a lot of people will be holding it from the corners of the bezel when they are holding it (sadly I don’t own one, but would like to) – and if this assumption is correct, then maybe my idea has some legs.

The current standard onscreen keyboard:

I am proposing a rethinking of that keyboard to something like this:

This would facilitate thumb typing a la iPod even given that your hands are quite far apart and matches the split ergonomic keyboard designs.  You could even add the whole keyboard in each corner, if some people are “hunt-and-peck” typers and would prefer to have either thumb reach for specific letters.

So hey! Apple, if you like this idea and decide to ever incorporate this into some next gen OS, I’d be happy if you sent me an iPad unit and/or some really small percentage of OS upgrade proceeds.

Googled around after I mocked this up and found several people mulling this over:

• A pretty well thought-out version written out here
• Scot Robbin’s split space bar in Concept: iPad Split Keyboard. 
• Duplicate keyboard design over at lonelysandwich.  
• A curved keypad, neat looking.