Don't worry about it. Learn Python well and you will be future proof, at least as a developer.
I've got active projects in both code bases right now - although I prefer Python 2.7 because it has taken a while for the libraries and frameworks to move over to 3.0.
However, once you understand the core concepts behind Python, about 90% of the differences between the two become obvious and trivial to work around for most projects.
You should get some exposure to 3.x since Guido has indicated any significant new language features will be implemented in that branch and not back-ported to 2.7. They have also done a number of optimizations in the 3.x branch which may be of interest for certain projects.