Yes. Like any other Python 2 releases, there are always new syntax and function additions. I think the only major Python library people use not available on Python 3 is Twisted. (edit: I think Mercurial is also not compatible with Python 3 IRRC due to byte-string and unicode incompatibility). Even Tornado and pyCurl works with Python 3 (according to pypi and doc).
Before you start writing in Python 3, make sure your dependencies will run on Python 3.
Before you start writing in Python 3, make sure your dependencies will run on Python 3.