At the end of 2013/beginning of 2014, a survey was conducted to see how much 3.x is catching on.
The survey itself is here. Note that recent takers of the survey will not see their results in the PDF below.
You can find the results here in PDF format: 2013-2014 Python 2.x-3.x survey.pdf.
Results as a single chart, unfortunately you need to mouse over the labels to see the full question text.