There is now an Ubuntu PPA for Obnam, with packages uploaded by the awesome Chris Cormack of Koha fame.

His mail to the (very low volume) Obnam mailing list has details: http://lists.liw.fi/obnam@braawi.org/msg00013.html.

If you experience any problems with the packages, don't hesitate to mail me, or the Obnam mailing list, or tell us on the #obnam IRC channel on irc.oftc.net.