It is an issue of therblig motion and operational failure (fancy talk for people dropping a device). From a therblig standpoint, landscape is counter-intuitive for one hand operation and less balance.

If you try the device with one hand while texting or other operations that you do not want the KB open and would rather use the screen, it is a very big issue and will hurt the N900- IF they are also targeting smart phones users.

If Nokia is only targeting devs and tablet users, no harm no foul. I think that due to their pricing (device seems lower cost for what you get), they are targeting more than those folks.

They want smart phone users, but do not yet have the basic functions most smart phoners use all the time.

I expect Nokia to correct this issue quickly.