Several new-ish laptops (eg Dell Inspiron 14Z) use the Atheros AR8162 ethernet chip for their wired networking, and it appears that there is no driver in this kernel version (at least).
There is a driver available at
I have used compat-wireless-2012-09-01-pc.tar.bz2 with success.
which appears to work fine when compiled and loaded as per instructions.
I initially filed this problem downstream on Launchpad, as
which is apparently a duplicate of
One of the maintainers suggested I file an upstream bug as well.
Whoever said that was wrong in this case I think. It's up to Ubuntu what backports it ships in its 3.2 kernels