Edit: Have a look at this thread: (MSC Mode for XPS). It could be a good workaround for your problem. MSC mode is kind of oldschool, but fine for copying things around.
If you want MTP support on Ubuntu, try this:
Connect Xperia S to an ...
Same problem here.
I get the blue LED light and a "S1Boot Fastboot" Device. Some seconds later, the device switches to some kind of charging mode and "S1Boot Fastboot" will turn in "Unknown device".
When i try to install the drivers with "Update...