I went to 3.3 a while ago but reverted back to 2.7 because out of the 10 or so crucial libraries I needed, one was still on 2.7. Bloomberg. (http://www.bloomberglabs.com/api/libraries/). That's what the people who talk about high percentages of libraries already ported to 3, miss. All you need is a single one not to be ported and the future stays on hold.

I have taken to using the 3 syntax in 2.7 so that I am prepared, but until this particular library moves, I cannot.