After we migrated to Python 3, we came to regret the decision with considerable regularity. We mostly use MacOS, and working with OpenGL and scientific libraries has been painful. We never found that a library we needed was not available for 2.7, but lots of stuff has not been ported to 3.3. The syntactic advantages of 3 have been too minor to warrant the troubles we earned. Your mileage may vary, if you have different applications, of course.