There's lots of reasons I find coding in Python 3 more enjoyable and productive. Unicode by default, removing x*() functions and returning generators where appropriate instead, removing old-style classes, improved consistency in standard object interfaces/protocols, standard lib cleanups, etc. Yes, even print() - keyword args are a lot nicer than the old hackish syntax for things like the output file.
These are often called minor and "no compelling reason to upgrade", but I'd submit that when a language does more often what you expect it to do, when the number of gotchas you need to keep in mind is reduced significantly, that's not minor. It might not be a reason to switch a large existing codebase over, but it's certainly a reason to write the next large codebase in it, and that's what Python 3 aims at: The future of Python and its future users.
No, that doesn't make for a fast transition, but indeed, it was never expected to be ("five years" is the plan, we're not there yet, and things look to be on track). Eventually, there just won't be any reasons left not to use Python 3, but plenty of reasons to do so (the better core language, the sum of improvements in the standard lib, the continued maintenance), and then it'll be done.