We definitely use it a Facebook, the linter suggests when you should use six instead.

There is also python-future which does similar things, I think.

Yes, and python-future does it in a more Pythonic was, it seems to me

It's disappointing to me that six.py hasn't yet made it into 2.7's standard library. That would definitely help enormously.

The standard library is where code goes to die. If six were in the standard library, it would be as stagnant and impossible to fix as 2to3.