Thought you might find this interesting/apropos: http://www.murrayc.com/blog/tech/2005-05-19-09-40.html According to http://live.gnome.org/ReleasesNotes2p12Items this is going to make it into GNOME 2.12. Looks like it might relieve part of your problem. I must admit that I do like spatial navigation in OS X -- it will be nice to have navigation in GNOME that doesn't break spatiality.
