Karmic has Postgres 8.4 as it’s default version, and 8.3 can prove tricky to install.
Unfortunately, not all of the contrib packages were upgraded to run on the new version in time.
One of these is postgis, the geodatabase extensions. You have two options, build it from source, or install the Lucid (10.4) package.
Obviously, Lucid isn’t released yet, but I have had success with just installing the package. Your Mileage May Vary.
Hope this helps someone!