Getting ssh to work on GNOME systems
Some GNOME users may find that the card works on their system but there is a problem with getting ssh subkeys on the card to work.
This is a problem causes by gnome-keyring. This application is taking control of the ssh socket and preventing gpg-agent from working properly.
You can fix this by issuing the following command in a terminal:
command> gconftool-2 --set -t bool /apps/gnome-keyring/daemon-components/ssh false
This fix for this problem was originally discussed here: http://www.gossamer-threads.com/lists/gnupg/users/43682