not .xinitrc, gnome session startup incompatibility
I did some additional testing to figure out what is wrong.
1/ boot on debian
1.1/ create a user "test" on the FC7 mounted partition, OK
1.2/ login as "test" with gdm, OK
1.3/ list home dir, gnome has created some dir/file
2/ boot on FC7
2.1/ create the same user "test" (same uid,gid), OK
2.2/ login as "test" with gdm, OK
2.3/ list home dir, gnome has updated and created some dir/file
3/ boot on debian
3.1/ login as "test" with gdm, OK
1.3/ list home dir, gnome has updated some dir/file
At this point, I am sure that basic gnome session is sharable between debian and fedora.
4/ I continue on debian
4.1 login as "FC7 user" with gdm, wait and finaly see that the login session is very slow. All gnome session step passed but at the end the screen is empty, only gkrellm visible (no activity), cannot switch on any virtual console (Ctrl+Alt+1, ...)
4.2/ take a coffee ....
4.3/ when back I get the lock screen and can switch to a debian user, everything seems OK for this session excepted virtual console still unavailable, 'ps -aef' show some missing process comparing debian user session and FC7 user session: metacity, gnome-panel, nautilus, ...
I think the problem comes from fedora user having special setup (applet, ...) which break debian gnome session startup.
I will investigate gnome session startup