When I click on a .deb file through Dolphin, Kpackagekit asks me if I would like to install the package. I click "Yes" and then I'm greeted with the error "This function is not yet supported". The package installs fine using dpkg -i from konsole.

Update: Forgot to mention I'm running Kubuntu with KDE 4.6 RC1. Any ideas as to what might be causing this? Should I file a bug with my distro or with kpackagekit?

Use the synaptic, it is already there just download the GUI for it and off you go, KpackageKit is not stable, and be better of with synaptic test and tried.
http://packages.debian.org/search?keywords=synaptic

Thanks but no thanks. I've been using kpackagekit without much problem for some time now and I don't plan on switching to synaptic because of this one problem with .deb files. I'd rather sort this out or continue to use dpkg until a solution is found.