Latest Android devices, like Nexus 7, are using 2 different USB connexion modes : PTP and MTP.
With PTP mode, the tablet is seen as a digital camera. This is working Out Of The Box under Ubuntu 12.04. But, you can only access DCIM directory of your device.
With MTP mode, the tablet is seen as a multimedia device where you can access the complete exported filesystem. But it doesn't work Out Of The Box under Ubuntu 12.04. It needs some setup and configuration to work.
Even if you can access easily a MTP device thru a program called gmtp, it is not as convenient as a conventional USB mass storage, accessible directly from Nautilus.
This guide explains how to configure your Ubuntu computer to directly access your Nexus 7 exported filesystem in MTP mode as soon as you plug it to a USB port.
Thanks to some udev rules, your Nexus 7 will automatically mount when device is plugged in & unmount when device is unplugged.
This guide has been done for Google Nexus 7, but it should work with any other MTP device (Android phone or tablet, MP4 player, ...) if you adapt the Udev rules according to your device.
I've got some feedback that it has already been adapted succesfully to Samsung Galaxy S2, Galaxy S3, Motorola Atrix HD & Google Nexus 4.
It has been done under Ubuntu 12.04, but has also been tested succesfully under Ubuntu 12.10.