Second, most software of any complexity will have dependencies. Although progress has been made, several packages that many projects depend upon are still red:
P.S. I'm the author of Python Primer on pythonmonk.com
HOWEVER, there are many important 3rd party libraries that have not yet been migrated to be fully compatible with Python 3. these libraries are far more important to writing real applications than the ability to use some newer syntactic constructs in Python 3.
Are there any particular libraries blocking you? Numpy / SciPy, IPython, Requests, Django, Pyramid, Bottle, etc. have all been ported to Python 3.
PIL as well. similar reasons. django image fields are dependent on PIL.
Celery is still on Python 2 also, and while there are other message queues available, none of them is as easy to integrate with for an app that's already written in Python.