Looks like I had to logout and login to complete the update to v0.8.

My laptop was installed as Gusty, later upgraded to Hardy and recently upgraded to Intrepid. In Synaptic I still only saw v0.6.1. I had to add the deb and deb-src repositories as above substituting intrepid for hardy. I also had to install the appropriate gpg key to stop apt-get update from complaining. After installing the 0.8 version and verifying the version in Synaptic, when I open Gnome-Do and click on About Do, it still says version 0.6.1. I'm guessing they forgot to update the About message.