For what is this empty space? I've noticed that N900 can detect touches in this area but it's just not emitting them. Like in the browser if you swipe your finger from the right end to the left end it will enter browsing history. And the way how you bring the cursor, except you're doing it on the left side. I taught that maybe if n900 really can detect touches in that areas, nokia will maybe in some update put like in N97 those green and red icons. like if you press the right side, it will hand up the call or whatever, and if you press on the left side, it will bring up the dialing pad. That would be really usefull, But if N900 really can't detect touches in that area, i don't know why nokia left that space empty...

mhm... we (as humans) like symmetry (our bodies are symmetric as well).
if something is only a bit assymmetric we'll recognize it in a blink of an eye ^^
and because the n900 is mostly used in landscape-view the area at the left and the right should be the same size.

in addition the screen has a fix aspect ratio and is a compromise between size, resolution and cost. so this is a fix size. and now look at the qwerty and all the stuff the n900 contains. (cpu, wifi, ir- and fm-transmitter, etc). you need space for that all - especially for the qwerty - it shouldn't be too small, right?

my conclusion:
it's a compromise between design and functionallity. ^^

Oh sorry, i totally forgot about wifi, bluetooth, and other...