With Android 3.x Google switch to MTP, a Microsoft's protocol for media transfer. That turned out to be bad news for GNU/Linux users as MTP is badly broken in the Linux userland. Canonical while did not waste any time in porting Ubuntu to Nexus 7 they did nothing to make life easier for Android-Ubuntu users.
The KDE developers stepped in.
A KDE developer, Àlex Fiestas, recently infromed me that he has added support for MTP devices to Dolphin. He used Philipp Schmidt’s MTP kioslave.
I just tested it with my Nexus 7 and Kubuntu 12.10 and it just works. Kudos to the KDE team for doing what users need.
If you want to install it on Kubuntu just add this PPA
sudo apt-add-repository ppa:philschmidt/ppa-kio-mtp-daily
sudo apt-get update
sudo apt-get install kio-mtp
Now plug in your Android device and you will be able to manage it from within Dolphin.