How do I use SSH keys for passwordless SSH via X11 apps (like nautilus)?

I've just reinstalled Ubuntu 10.10 on my laptop, and I'm trying to get SSH pubkey authentication working via X11 applications. Specifically, I'm trying to use baobab to display the usage of a remote filesystem, and I need to SSH in as root but root has no password, so I need to use an SSH key to authenticate. In the terminal, if I ssh root@theserver, I get right in with no password, but if I use Baobab or Nautilus to connect, it asks me for my password. How can I have it use my SSH key? I'm using GNOME in case it matters. On my previous install this worked, and I don't know if I did something before to make it work. If so, I've forgotten what… In fact, my previous install would pop up an X11 dialog asking for my SSH private key password if I needed to unlock it. How do I make that happen again?