If you were starting to build new web apps in Python today, would you go with Python 2.7 or Python 3.x at this point?
For a quick hack I'd still use 2.7 because everything is compatible so it should be easier to get up and running.
I've built a couple small web apps, a few small PyQt apps, and a ton of utilities with it.
Only times I've used 2.x recently was when I needed OpenGL, and another time when I needed cgkit.
Basically the only time I use 2 is when I need a specific library and there's no alternative that runs on 3.
The switching point for me will be when django start support 3.x. Looks like Django 1.5 will add experimental support for Python 3.x. Then there will take at least a couple months for most of the vital packages to be compatible.
However, I much prefer 3.x. Much cleaner, better stdlib, and unicode everything. If you do use 2.7, please please please use 3.x printing though (from __future__ import print_function)