For what it's worth, the examples from Mark's book still compile with Python 2.7 and the latest PyQt bindings. And PyQt itself comes with examples that are stored in Python\lib\site-packages\pyqt4\examples\ . I don't think a lot has changed that breaks backward-compatibility since the book was published.
I don't really know what benefits you would have from Python 3.x, I think 2.7 got some 3.x features backported to that version as well..
