In the long term I think we need both 2to3 and 3to2, but for now 2to3 is more important. As long as both my dependencies and the users of my library are mostly on 2.x, I want that to be my primary development platform. If the only way to support both platforms was to do most of my work in python 3 and then backport to 2.x, I'd have never gotten started because that's too much of a change to take on at once. 2to3 gives me a way to support 3.x now (even as a second class citizen), and then a path to flip things around and make 3.x the primary platform when I'm ready.
I just find the "for now" pretty hilarious: we are already seeing a shipping version of Python 3.2, with Python 3.x having been released for years, and we still need to encourage people to develop code for Python 2.x and use a build step to convert their code to Python 3.x. The effect of this attitude directly contributes to the behavior described in that recent article by the Jinja2 developer: where Python 3.x support is often considered by people to be just "look, I did it, and while it is a horrible hack and much slower than the 2.x version, it sort of works; now leave me alone", as opposed to helping people slowly embrace Python 3.x.
