user@client:~$ uname -a
Linux client 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:57:59 UTC 2009 i686 GNU/Linux
user@client:~$ ssh -i .ssh/id_rsa server
user@server's password: ^C 

user@client:~$ SSH_AUTH_SOCK=0 ssh -i .ssh/id_rsa server
Enter passphrase for key '.ssh/id_rsa': 
Linux server.domain.tld 2.6.24-etchnhalf.1-amd64 #1 SMP Fri Dec 26 03:26:12 UTC 2008 x86_64
user@server:~$ logout
Connection to server closed.
user@client:~$ env | grep -i SSH
SSH_AGENT_PID=6894
SSH_AUTH_SOCK=/tmp/keyring-WjatFa/socket.ssh
user@client:~$ ps uax | grep [6]894
user  6894  0.0  0.0   4784   604 ?        Ss   Apr30   0:00 /usr/bin/ssh-agent /usr/bin/dbus-launch --exit-with-session /usr/bin/pulse-session /usr/bin/seahorse-agent --execute x-session-manager
user@client:~$ dpkg -l | grep seahorse
ii  seahorse                                   2.26.1-0ubuntu1                         A Gnome front end for GnuPG
ii  seahorse-plugins                           2.26.1-0ubuntu1                         seahorse plugins and utilities for encryptio