If you want your phone to stay in portrait mode in bed, you'd use the new screen orientation lock feature in GDR 3, so that would prevent the home screen from rotating (if it were able to to so).
I find myself using my Symbian phone's home screen in landscape mode when it is mounted in my car. I use Car Mode and Nokia Here maps for navigation, obviously, in landscape mode, because that's the better orientation for car mounting. Then e.g. when I get into a traffic jam and nothing is happening on the road I leave the phone in the mount but press the home button to get to the start screen, have a quick look at new incoming mail etc.That's OK and safe, but obviously, while driving, I would not want to remove my phone from the mount and hold it in my hands just to have it in portrait mode so as to be able to use the homescreen ...
To me, the home screen not being available in landscape mode in Windows Phone is a big showstopper that makes we want to stay with Symbian as long as possible.
Frankly, I cannot understand why users keep discussing about the usefulness of a feature. ANY feature that was there in other, older mobile OSes was useful to SOMEONE, and SOMEONE has grown attached to it for sure and will miss it in WP if it is not there. The goal should be to make Windows Phone as feature complete as possible. (If you want a minimalistic feature set, you'd be using iOS anyway ...).