Please remember there are several things this does not mean:
Python 2.x is not obsolete. The series will continue through 2.6 (which will include backports of many Python 3 features) and probably 2.7. In fact the only guarantee is that there will be no releases after 2.9.x, as Guido has stated his dislike of the ambiguities inherent in a 2.10 release number.
Python 3 is not ready for production work. The alpha series is expected to last a considerable length of time, and even when Python 3 comes into production (in around a year from now if Guido's original schedule is maintained) 2.6 will be the major platform.
There should be no need to develop parallel source trees for your Python code. The 2.6 translator will have a "Python 3 warnings" mode, and if you ensure that this doesn't produce warnings you will be able to convert your code to Python 3 automatically using a conversion tool.
For a summary of other things you might like to know about Python 3 see Guido's blog.
Please remember there are several things this does not mean: