Using ssh-add in Gnome
ssh-add is neat but it is only valid for a single terminal session. To save you entering your passphrase every time when using Gnome, install openssh-askpass and add the following to Gnome's startup programs (System > Preferences > More Preferences > Sessions > Startup Programs) "/usr/bin/ssh-add". You will be prompted for your passphrase when logging in to Gnome.