Are you targeting a specific physical size with the concepts? Like someone else said, that device looks fairly big. It seems reasonable that what is best for a big display might not be best for a small one.

Also, as a general suggestion, one of the -worst- things about the current desktop is manual window management - please, please come up with an automatic system that works! The iPhone sidesteps this by only allowing one app at a time, but with several apps it'll be one of the make-or-break aspects of these devices...